Temporal Identifier Constraints For SEI Messages

ABSTRACT

A video coding mechanism is disclosed. The mechanism includes encoding a coded picture in one or more video coding layer (VCL) network abstraction layer (NAL) units in a bitstream. A non-VCL NAL unit is encoded into the bitstream such that a temporal identifier (TemporalId) for the non-VCL NAL unit is constrained to be equal to a TemporalId of an access unit (AU) containing the non-VCL NAL unit when a NAL unit type (nal_unit_type) of the non-VCL NAL indicates a supplemental enhancement information (SEI) message. A set of bitstream conformance tests is performed on the bitstream based on the SEI message. The bitstream is stored for communication toward a decoder.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of International ApplicationNo. PCT/US2020/051313, filed Sep. 17, 2020 by Ye-Kui Wang, and titled“Temporal Identifier Constraints For SEI Messages,” which claims thebenefit of U.S. Provisional Patent Application No. 62/905,236 filed Sep.24, 2019 by Ye-Kui Wang, and titled “Video Coding Improvements,” whichare hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure is generally related to video coding, and isspecifically related to improvements in signaling parameters to supportcoding of multi-layer bitstreams.

BACKGROUND

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in image qualityare desirable.

SUMMARY

In an embodiment, the disclosure includes a method implemented by adecoder, the method comprising: receiving, by a receiver of the decoder,a bitstream comprising a coded picture in one or more video coding layer(VCL) network abstraction layer (NAL) units and a non-VCL NAL unit,wherein a temporal identifier (TemporalId) for the non-VCL NAL unit isconstrained to be equal to a TemporalId of an access unit (AU)containing the non-VCL NAL unit when a NAL unit type (nal_unit_type) ofthe non-VCL NAL is equal to a prefix supplemental enhancementinformation (SEI) NAL unit type (PREFIX_SEI_NUT) or a suffix SEI NALunit type (SUFFIX_SEI_NUT); deriving, by a processor of the decoder, theTemporalId for the non-VCL NAL unit based on a NAL unit header temporalidentifier plus one (nuh_temporal_id_plus1) syntax element in thenon-VCL NAL unit; and decoding, by the processor of the decoder, thecoded picture from the VCL NAL units to produce a decoded picture.

A video sequence can include many pictures. To ensure the pictures aredisplayed in the correct order, video coding systems may assign thepictures a TemporalId. Some video coding systems employ layers ofpictures, where each layer includes substantially the same video atdifferent resolutions, picture sizes, frame rates, etc. Pictures indifferent layers may be displayed in the alternative, dependingconditions at the decoder. Accordingly, pictures in different layersthat are positioned at the same point in the video sequence share thesame TemporalId. Further, pictures in different layers that share thesame TemporalId make up an AU. For example, a decoder may display asingle picture selected from a single layer at each AU to display avideo sequence. Some video coding systems employ SEI messages. An SEImessage contains information that is not needed by the decoding processin order to determine the values of the samples in decoded pictures. Forexample, the SEI messages may contain parameters used by a hypotheticalreference decoder (HRD) operating at an encoder to check a bitstream forconformance with standards. Further, the video coding systems may code avideo sequence into the bitstream as layers of pictures. The SEImessages may be related to varying pictures and/or varying combinationsof layers. Accordingly, ensuring that the proper SEI message isassociated with the proper pictures/layers can become challenging incomplex multi-layer bitstreams. In the event that an SEI message is notassociated with the correct layer/picture, the HRD may be unable toproperly check the layer/picture for conformance. This may result inencoding errors.

The present example includes a mechanism for correctly associating SEImessages to corresponding pictures/layers. Multilayer bitstreams mayorganize pictures and associated parameters into AUs. An AU is a set ofcoded pictures that are included in different layers and are associatedwith the same output time. An SEI message may be positioned in the sameAU as the first picture associated with the SEI message. Further, theSEI message is assigned a TemporalId. A TemporalId is an identifier thatindicates the relative position of a NAL unit in a video sequence. TheTemporalId of the SEI message is constrained to be equal to theTemporalId of the AU that contains the SEI message. Stated differently,the pictures are included in VCL NAL units and parameters are includedin non-VCL NAL units. When the non-VCL NAL unit is an SEI NAL unitcontaining an SEI message, the TemporalId of the non-VCL NAL unit isconstrained to be equal to the TemporalId of the AU containing thenon-VCL NAL unit. This approach ensures that the SEI messages arecorrectly associated with corresponding pictures in the AUs. Hence,various errors may be avoided. As a result, the functionality of theencoder and the decoder is improved. Further, coding efficiency may beincreased, which reduces processor, memory, and/or network signalingresource usage at both the encoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the nal_unit_type of the non-VCL NAL isequal to the PREFIX_SEI_NUT.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the nal_unit_type of the non-VCL NAL isequal to the SUFFIX_SEI_NUT.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the coded picture is decoded from the VCLNAL units based on a SEI message in the non-VCL NAL unit.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, further comprising deriving the TemporalId for thenon-VCL NAL unit as follows:

TemporalId = nuh_temporal_id_plus1 − 1.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein a value of nuh_temporal_id_plus1 is notequal to zero.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein a TemporalId of the VCL NAL units isconstrained to be the same for all VCL NAL units in a same AU.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, further comprising: receiving, by the decoder, asecond bitstream including a second one or more VCL NAL units and asecond non-VCL NAL unit, wherein a TemporalId for the second non-VCL NALunit is not equal to a TemporalId of a second AU containing the secondnon-VCL NAL unit when a nal_unit_type of the second non-VCL NAL is a SEImessage; and in response to the receiving, taking some other correctivemeasures to ensure that a conforming bitstream corresponding to thesecond bitstream is received prior to decoding the coded picture fromthe second VCL NAL units.

In an embodiment, the disclosure includes a method implemented by anencoder, the method comprising: encoding, by a processor of the encoder,a coded picture in one or more VCL NAL units in a bitstream; encodinginto the bitstream, by the processor, a non-VCL NAL unit such that anuh_temporal_id_plus1 for the non-VCL NAL unit is constrained to beequal to a nuh_temporal_id_plus1 of an AU containing the non-VCL NALunit when a nal_unit_type of the non-VCL NAL is a SEI message;performing, by the processor, a set of bitstream conformance tests onthe bitstream based on the SEI message; and storing, by a memory coupledto the processor, the bitstream for communication toward a decoder.

A video sequence can include many pictures. To ensure the pictures aredisplayed in the correct order, video coding systems may assign thepictures a TemporalId. Some video coding systems employ layers ofpictures, where each layer includes substantially the same video atdifferent resolutions, picture sizes, frame rates, etc. Pictures indifferent layers may be displayed in the alternative, dependingconditions at the decoder. Accordingly, pictures in different layersthat are positioned at the same point in the video sequence share thesame TemporalId. Further, pictures in different layers that share thesame TemporalId make up an AU. For example, a decoder may display asingle picture selected from a single layer at each AU to display avideo sequence. Some video coding systems employ SEI messages. An SEImessage contains information that is not needed by the decoding processin order to determine the values of the samples in decoded pictures. Forexample, the SEI messages may contain parameters used by a hypotheticalreference decoder (HRD) operating at an encoder to check a bitstream forconformance with standards. Further, the video coding systems may code avideo sequence into the bitstream as layers of pictures. The SEImessages may be related to varying pictures and/or varying combinationsof layers. Accordingly, ensuring that the proper SEI message isassociated with the proper pictures/layers can become challenging incomplex multi-layer bitstreams. In the event that an SEI message is notassociated with the correct layer/picture, the HRD may be unable toproperly check the layer/picture for conformance. This may result inencoding errors.

The present example includes a mechanism for correctly associating SEImessages to corresponding pictures/layers. Multilayer bitstreams mayorganize pictures and associated parameters into AUs. An AU is a set ofcoded pictures that are included in different layers and are associatedwith the same output time. An SEI message may be positioned in the sameAU as the first picture associated with the SEI message. Further, theSEI message is assigned a TemporalId. A TemporalId is an identifier thatindicates the relative position of a NAL unit in a video sequence. TheTemporalId of the SEI message is constrained to be equal to theTemporalId of the AU that contains the SEI message. Stated differently,the pictures are included in VCL NAL units and parameters are includedin non-VCL NAL units. When the non-VCL NAL unit is an SEI NAL unitcontaining an SEI message, the TemporalId of the non-VCL NAL unit isconstrained to be equal to the TemporalId of the AU containing thenon-VCL NAL unit. This approach ensures that the SEI messages arecorrectly associated with corresponding pictures in the AUs. Hence,various errors may be avoided. As a result, the functionality of theencoder and the decoder is improved. Further, coding efficiency may beincreased, which reduces processor, memory, and/or network signalingresource usage at both the encoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the nal_unit_type of the non-VCL NAL isequal to a PREFIX_SEI_NUT.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the nal_unit_type of the non-VCL NAL isequal to a SUFFIX_SEI_NUT.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein a value of nuh_temporal_id_plus1 is notequal to zero.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein a nuh_temporal_id_plus1 of the VCL NALunits is constrained to be the same for all VCL NAL units in a same AU.

In an embodiment, the disclosure includes a video coding devicecomprising: a processor, a receiver coupled to the processor, a memorycoupled to the processor, and a transmitter coupled to the processor,wherein the processor, receiver, memory, and transmitter are configuredto perform the method of any of the preceding aspects.

In an embodiment, the disclosure includes a non-transitory computerreadable medium comprising a computer program product for use by a videocoding device, the computer program product comprising computerexecutable instructions stored on the non-transitory computer readablemedium such that when executed by a processor cause the video codingdevice to perform the method of any of the preceding aspects.

In an embodiment, the disclosure includes a decoder comprising: areceiving means for receiving a bitstream comprising a coded picture inone or more VCL NAL units and a non-VCL NAL unit, wherein a TemporalIdfor the non-VCL NAL unit is constrained to be equal to a TemporalId ofan AU containing the non-VCL NAL unit when a nal_unit_type of thenon-VCL NAL is a SEI message; a decoding means for decoding the codedpicture from the VCL NAL units to produce a decoded picture; and aforwarding means for forwarding the decoded picture for display as partof a decoded video sequence.

A video sequence can include many pictures. To ensure the pictures aredisplayed in the correct order, video coding systems may assign thepictures a TemporalId. Some video coding systems employ layers ofpictures, where each layer includes substantially the same video atdifferent resolutions, picture sizes, frame rates, etc. Pictures indifferent layers may be displayed in the alternative, dependingconditions at the decoder. Accordingly, pictures in different layersthat are positioned at the same point in the video sequence share thesame TemporalId. Further, pictures in different layers that share thesame TemporalId make up an AU. For example, a decoder may display asingle picture selected from a single layer at each AU to display avideo sequence. Some video coding systems employ SEI messages. An SEImessage contains information that is not needed by the decoding processin order to determine the values of the samples in decoded pictures. Forexample, the SEI messages may contain parameters used by a hypotheticalreference decoder (HRD) operating at an encoder to check a bitstream forconformance with standards. Further, the video coding systems may code avideo sequence into the bitstream as layers of pictures. The SEImessages may be related to varying pictures and/or varying combinationsof layers. Accordingly, ensuring that the proper SEI message isassociated with the proper pictures/layers can become challenging incomplex multi-layer bitstreams. In the event that an SEI message is notassociated with the correct layer/picture, the HRD may be unable toproperly check the layer/picture for conformance. This may result inencoding errors.

The present example includes a mechanism for correctly associating SEImessages to corresponding pictures/layers. Multilayer bitstreams mayorganize pictures and associated parameters into AUs. An AU is a set ofcoded pictures that are included in different layers and are associatedwith the same output time. An SEI message may be positioned in the sameAU as the first picture associated with the SEI message. Further, theSEI message is assigned a TemporalId. A TemporalId is an identifier thatindicates the relative position of a NAL unit in a video sequence. TheTemporalId of the SEI message is constrained to be equal to theTemporalId of the AU that contains the SEI message. Stated differently,the pictures are included in VCL NAL units and parameters are includedin non-VCL NAL units. When the non-VCL NAL unit is an SEI NAL unitcontaining an SEI message, the TemporalId of the non-VCL NAL unit isconstrained to be equal to the TemporalId of the AU containing thenon-VCL NAL unit. This approach ensures that the SEI messages arecorrectly associated with corresponding pictures in the AUs. Hence,various errors may be avoided. As a result, the functionality of theencoder and the decoder is improved. Further, coding efficiency may beincreased, which reduces processor, memory, and/or network signalingresource usage at both the encoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the decoder is further configured toperform the method of any of the preceding aspects.

In an embodiment, the disclosure includes an encoder comprising: anencoding means for: encoding a coded picture in one or more VCL NALunits in a bitstream; and encoding into the bitstream a non-VCL NAL unitsuch that a TemporalId for the non-VCL NAL unit is constrained to beequal to a TemporalId of an AU containing the non-VCL NAL unit when anal_unit_type of the non-VCL NAL is a supplemental SEI message; a HRDmeans for performing a set of bitstream conformance tests on thebitstream based on the SEI message; and a storing means for storing thebitstream for communication toward a decoder.

A video sequence can include many pictures. To ensure the pictures aredisplayed in the correct order, video coding systems may assign thepictures a TemporalId. Some video coding systems employ layers ofpictures, where each layer includes substantially the same video atdifferent resolutions, picture sizes, frame rates, etc. Pictures indifferent layers may be displayed in the alternative, dependingconditions at the decoder. Accordingly, pictures in different layersthat are positioned at the same point in the video sequence share thesame TemporalId. Further, pictures in different layers that share thesame TemporalId make up an AU. For example, a decoder may display asingle picture selected from a single layer at each AU to display avideo sequence. Some video coding systems employ SEI messages. An SEImessage contains information that is not needed by the decoding processin order to determine the values of the samples in decoded pictures. Forexample, the SEI messages may contain parameters used by a hypotheticalreference decoder (HRD) operating at an encoder to check a bitstream forconformance with standards. Further, the video coding systems may code avideo sequence into the bitstream as layers of pictures. The SEImessages may be related to varying pictures and/or varying combinationsof layers. Accordingly, ensuring that the proper SEI message isassociated with the proper pictures/layers can become challenging incomplex multi-layer bitstreams. In the event that an SEI message is notassociated with the correct layer/picture, the HRD may be unable toproperly check the layer/picture for conformance. This may result inencoding errors.

The present example includes a mechanism for correctly associating SEImessages to corresponding pictures/layers. Multilayer bitstreams mayorganize pictures and associated parameters into AUs. An AU is a set ofcoded pictures that are included in different layers and are associatedwith the same output time. An SEI message may be positioned in the sameAU as the first picture associated with the SEI message. Further, theSEI message is assigned a TemporalId. A TemporalId is an identifier thatindicates the relative position of a NAL unit in a video sequence. TheTemporalId of the SEI message is constrained to be equal to theTemporalId of the AU that contains the SEI message. Stated differently,the pictures are included in VCL NAL units and parameters are includedin non-VCL NAL units. When the non-VCL NAL unit is an SEI NAL unitcontaining an SEI message, the TemporalId of the non-VCL NAL unit isconstrained to be equal to the TemporalId of the AU containing thenon-VCL NAL unit. This approach ensures that the SEI messages arecorrectly associated with corresponding pictures in the AUs. Hence,various errors may be avoided. As a result, the functionality of theencoder and the decoder is improved. Further, coding efficiency may beincreased, which reduces processor, memory, and/or network signalingresource usage at both the encoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the encoder is further configured toperform the method of any of the preceding aspects.

For the purpose of clarity, any one of the foregoing embodiments may becombined with any one or more of the other foregoing embodiments tocreate a new embodiment within the scope of the present disclosure.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a flowchart of an example method of coding a video signal.

FIG. 2 is a schematic diagram of an example coding and decoding (codec)system for video coding.

FIG. 3 is a schematic diagram illustrating an example video encoder.

FIG. 4 is a schematic diagram illustrating an example video decoder.

FIG. 5 is a schematic diagram illustrating an example hypotheticalreference decoder (HRD).

FIG. 6 is a schematic diagram illustrating an example multi-layer videosequence.

FIG. 7 is a schematic diagram illustrating an example bitstream.

FIG. 8 is a schematic diagram of an example video coding device.

FIG. 9 is a flowchart of an example method of encoding a video sequenceinto a bitstream by constraining temporal identifiers (TemporalIds) forsupplemental enhancement information (SEI) messages in the bitstream.

FIG. 10 is a flowchart of an example method of decoding a video sequencefrom a bitstream where TemporalIds for the SEI messages in the bitstreamare constrained.

FIG. 11 is a schematic diagram of an example system for coding a videosequence using a bitstream where TemporalIds for the SEI messages in thebitstream are constrained.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

The following terms are defined as follows unless used in a contrarycontext herein. Specifically, the following definitions are intended toprovide additional clarity to the present disclosure. However, terms maybe described differently in different contexts. Accordingly, thefollowing definitions should be considered as a supplement and shouldnot be considered to limit any other definitions of descriptionsprovided for such terms herein.

A bitstream is a sequence of bits including video data that iscompressed for transmission between an encoder and a decoder. An encoderis a device that is configured to employ encoding processes to compressvideo data into a bitstream. A decoder is a device that is configured toemploy decoding processes to reconstruct video data from a bitstream fordisplay. A picture is an array of luma samples and/or an array of chromasamples that create a frame or a field thereof. A slice is an integernumber of complete tiles or an integer number of consecutive completecoding tree unit (CTU) rows (e.g., within a tile) of a picture that areexclusively contained in a single network abstraction layer (NAL) unit.A picture that is being encoded or decoded can be referred to as acurrent picture for clarity of discussion. A coded picture is a codedrepresentation of a picture comprising video coding layer (VCL) NALunits with a particular value of NAL unit header layer identifier(nuh_layer_id) within an access unit (AU) and containing all coding treeunits (CTUs) of the picture. A decoded picture is a picture produced byapplying a decoding process to a coded picture.

An AU is a set of coded pictures that are included in different layersand are associated with the same time for output from a decoded picturebuffer (DPB). A NAL unit is a syntax structure containing data in theform of a Raw Byte Sequence Payload (RBSP), an indication of the type ofdata, and interspersed as desired with emulation prevention bytes. A VCLNAL unit is a NAL unit coded to contain video data, such as a codedslice of a picture. A non-VCL NAL unit is a NAL unit that containsnon-video data such as syntax and/or parameters that support decodingthe video data, performance of conformance checking, or otheroperations. A NAL unit type (nal_unit_type) is a syntax elementcontained in a NAL unit that indicates a type of data contained in theNAL unit. A layer is a set of VCL NAL units that share a specifiedcharacteristic (e.g., a common resolution, frame rate, image size, etc.)as indicated by layer ID and associated non-VCL NAL units. A NAL unitheader layer identifier (nuh_layer_id) is a syntax element thatspecifies an identifier of a layer that includes a NAL unit. A temporalidentifier (TemporalId) is a derived identifier that indicates therelative position of a NAL unit in a video sequence. A NAL unit headertemporal identifier plus one (nuh_temporal_id_plus1) is a signaledidentifier that indicates the relative position of a NAL unit in a videosequence.

A hypothetical reference decoder (HRD) is a decoder model operating onan encoder that checks the variability of bitstreams produced by anencoding process to verify conformance with specified constraints. Abitstream conformance test is a test to determine whether an encodedbitstream complies with a standard, such as Versatile Video Coding(VVC). HRD parameters are syntax elements that initialize and/or defineoperational conditions of an HRD. HRD parameters may be included insupplemental enhancement information (SEI) messages and/or in a videoparameter set (VP S). A SEI message is a syntax structure with specifiedsemantics that conveys information that is not needed by the decodingprocess in order to determine the values of the samples in decodedpictures. A SEI NAL unit is a NAL unit that contains one or more SEImessages. A specific SEI NAL unit may be referred to as a current SEINAL unit. A scalable nesting SEI message is a message that contains aplurality of SEI messages that correspond to one or more output layersets (OLSs) or one or more layers. A buffering period (BP) SEI messageis a SEI message that contains HRD parameters for initializing an HRD tomanage a coded picture buffer (CPB). A picture timing (PT) SEI messageis a SEI message that contains HRD parameters for managing deliveryinformation for AUs at the CPB and/or a decoded picture buffer (DPB). Adecoding unit information (DUI) SEI message is a SEI message thatcontains HRD parameters for managing delivery information for DUs at theCPB and/or the DPB. A scalable nesting SEI message is a set ofscalable-nested SEI messages. A scalable-nested SEI message is a SEImessage that is nested inside a scalable nesting SEI message. A prefixSEI message is a SEI message that applies to one or more subsequent NALunits. A suffix SEI message is a SEI message that applies to one or morepreceding NAL units.

A picture parameter set (PPS) is a syntax structure containing syntaxelements that apply to entire coded pictures as determined by a syntaxelement found in each picture header. A picture header is a syntaxstructure containing syntax elements that apply to all slices of a codedpicture. A slice header is a part of a coded slice containing dataelements pertaining to all tiles or CTU rows within a tile representedin the slice. A coded video sequence is a set of one or more codedpictures. A decoded video sequence is a set of one or more decodedpictures.

The following acronyms are used herein, Access Unit (AU), Coding TreeBlock (CTB), Coding Tree Unit (CTU), Coding Unit (CU), Coded Layer VideoSequence (CLVS), Coded Layer Video Sequence Start (CLVSS), Coded VideoSequence (CVS), Coded Video Sequence Start (CVSS), Joint Video ExpertsTeam (JVET), Hypothetical Reference Decoder HRD, Motion Constrained TileSet (MCTS), Maximum Transfer Unit (MTU), Network Abstraction Layer(NAL), Output Layer Set (OLS), Picture Order Count (POC), Random AccessPoint (RAP), Raw Byte Sequence Payload (RBSP), Sequence Parameter Set(SPS), Video Parameter Set (VPS), Versatile Video Coding (VVC).

Many video compression techniques can be employed to reduce the size ofvideo files with minimal loss of data. For example, video compressiontechniques can include performing spatial (e.g., intra-picture)prediction and/or temporal (e.g., inter-picture) prediction to reduce orremove data redundancy in video sequences. For block-based video coding,a video slice (e.g., a video picture or a portion of a video picture)may be partitioned into video blocks, which may also be referred to astreeblocks, coding tree blocks (CTBs), coding tree units (CTUs), codingunits (CUs), and/or coding nodes. Video blocks in an intra-coded (I)slice of a picture are coded using spatial prediction with respect toreference samples in neighboring blocks in the same picture. Videoblocks in an inter-coded unidirectional prediction (P) or bidirectionalprediction (B) slice of a picture may be coded by employing spatialprediction with respect to reference samples in neighboring blocks inthe same picture or temporal prediction with respect to referencesamples in other reference pictures. Pictures may be referred to asframes and/or images, and reference pictures may be referred to asreference frames and/or reference images. Spatial or temporal predictionresults in a predictive block representing an image block. Residual datarepresents pixel differences between the original image block and thepredictive block. Accordingly, an inter-coded block is encoded accordingto a motion vector that points to a block of reference samples formingthe predictive block and the residual data indicating the differencebetween the coded block and the predictive block. An intra-coded blockis encoded according to an intra-coding mode and the residual data. Forfurther compression, the residual data may be transformed from the pixeldomain to a transform domain. These result in residual transformcoefficients, which may be quantized. The quantized transformcoefficients may initially be arranged in a two-dimensional array. Thequantized transform coefficients may be scanned in order to produce aone-dimensional vector of transform coefficients. Entropy coding may beapplied to achieve even more compression. Such video compressiontechniques are discussed in greater detail below.

To ensure an encoded video can be accurately decoded, video is encodedand decoded according to corresponding video coding standards. Videocoding standards include International Telecommunication Union (ITU)Standardization Sector (ITU-T) H.261, International Organization forStandardization/International Electrotechnical Commission (ISO/IEC)Motion Picture Experts Group (MPEG)-1 Part 2, ITU-T H.262 or ISO/IECMPEG-2 Part 2, ITU-T H.263, ISO/IEC MPEG-4 Part 2, Advanced Video Coding(AVC), also known as ITU-T H.264 or ISO/IEC MPEG-4 Part 10, and HighEfficiency Video Coding (HEVC), also known as ITU-T H.265 or MPEG-H Part2. AVC includes extensions such as Scalable Video Coding (SVC),Multiview Video Coding (MVC) and Multiview Video Coding plus Depth(MVC+D), and three dimensional (3D) AVC (3D-AVC). HEVC includesextensions such as Scalable HEVC (SHVC), Multiview HEVC (MV-HEVC), and3D HEVC (3D-HEVC). The joint video experts team (JVET) of ITU-T andISO/IEC has begun developing a video coding standard referred to asVersatile Video Coding (VVC). VVC is included in a Working Draft (WD),which includes JVET-O2001-v14.

A video sequence can include many pictures. To ensure the pictures aredisplayed in the correct order, video coding systems may assign thepictures a temporal identifier (TemporalId). Some video coding systemsemploy layers of pictures, where each layer includes substantially thesame video at different resolutions, picture sizes, frame rates, etc.Pictures in different layers may be displayed in the alternative,depending conditions at the decoder. Accordingly, pictures in differentlayers that are positioned at the same point in the video sequence sharethe same TemporalId. Further, pictures in different layers that sharethe same TemporalId make up an access unit (AU). For example, a decodermay display a single picture selected from a single layer at each AU todisplay a video sequence.

Some video coding systems employ SEI messages. An SEI message containsinformation that is not needed by the decoding process in order todetermine the values of the samples in decoded pictures. For example,the SEI messages may contain parameters used by a HRD operating at anencoder to check a bitstream for conformance with standards. Further,the video coding systems may code a video sequence into the bitstream aslayers of pictures. The SEI messages may be related to varying picturesand/or varying combinations of layers. Accordingly, ensuring that theproper SEI message is associated with the proper pictures/layers canbecome challenging in complex multi-layer bitstreams. In the event thatan SEI message is not associated with the correct layer/picture, the HRDmay be unable to properly check the layer/picture for conformance. Thismay result in encoding errors.

Disclosed herein is a mechanism for correctly associating SEI messagesto corresponding pictures/layers. Multilayer bitstreams may organizepictures and associated parameters into AUs. An AU is a set of codedpictures that are included in different layers and are associated withthe same output time. An SEI message may be positioned in the same AU asthe first picture associated with the SEI message. Further, the SEImessage is assigned a TemporalId. A TemporalId is an identifier thatindicates the relative position of a network abstraction layer (NAL)unit in a video sequence. The TemporalId of the SEI message isconstrained to be equal to the TemporalId of the AU that contains theSEI message. Stated differently, the pictures are included in videocoding layer (VCL) NAL units and parameters are included in non-VCL NALunits. When the non-VCL NAL unit is an SEI NAL unit containing an SEImessage, the TemporalId of the non-VCL NAL unit is constrained to beequal to the TemporalId of the AU containing the non-VCL NAL unit. Thisapproach ensures that the SEI messages are correctly associated withcorresponding pictures in the AUs. Hence, various errors may be avoided.As a result, the functionality of the encoder and the decoder isimproved. Further, coding efficiency may be increased, which reducesprocessor, memory, and/or network signaling resource usage at both theencoder and the decoder.

FIG. 1 is a flowchart of an example operating method 100 of coding avideo signal. Specifically, a video signal is encoded at an encoder. Theencoding process compresses the video signal by employing variousmechanisms to reduce the video file size. A smaller file size allows thecompressed video file to be transmitted toward a user, while reducingassociated bandwidth overhead. The decoder then decodes the compressedvideo file to reconstruct the original video signal for display to anend user. The decoding process generally mirrors the encoding process toallow the decoder to consistently reconstruct the video signal.

At step 101, the video signal is input into the encoder. For example,the video signal may be an uncompressed video file stored in memory. Asanother example, the video file may be captured by a video capturedevice, such as a video camera, and encoded to support live streaming ofthe video. The video file may include both an audio component and avideo component. The video component contains a series of image framesthat, when viewed in a sequence, gives the visual impression of motion.The frames contain pixels that are expressed in terms of light, referredto herein as luma components (or luma samples), and color, which isreferred to as chroma components (or color samples). In some examples,the frames may also contain depth values to support three dimensionalviewing.

At step 103, the video is partitioned into blocks. Partitioning includessubdividing the pixels in each frame into square and/or rectangularblocks for compression. For example, in High Efficiency Video Coding(HEVC) (also known as H.265 and MPEG-H Part 2) the frame can first bedivided into coding tree units (CTUs), which are blocks of a predefinedsize (e.g., sixty-four pixels by sixty-four pixels). The CTUs containboth luma and chroma samples. Coding trees may be employed to divide theCTUs into blocks and then recursively subdivide the blocks untilconfigurations are achieved that support further encoding. For example,luma components of a frame may be subdivided until the individual blockscontain relatively homogenous lighting values. Further, chromacomponents of a frame may be subdivided until the individual blockscontain relatively homogenous color values. Accordingly, partitioningmechanisms vary depending on the content of the video frames.

At step 105, various compression mechanisms are employed to compress theimage blocks partitioned at step 103. For example, inter-predictionand/or intra-prediction may be employed. Inter-prediction is designed totake advantage of the fact that objects in a common scene tend to appearin successive frames. Accordingly, a block depicting an object in areference frame need not be repeatedly described in adjacent frames.Specifically, an object, such as a table, may remain in a constantposition over multiple frames. Hence the table is described once andadjacent frames can refer back to the reference frame. Pattern matchingmechanisms may be employed to match objects over multiple frames.Further, moving objects may be represented across multiple frames, forexample due to object movement or camera movement. As a particularexample, a video may show an automobile that moves across the screenover multiple frames. Motion vectors can be employed to describe suchmovement. A motion vector is a two-dimensional vector that provides anoffset from the coordinates of an object in a frame to the coordinatesof the object in a reference frame. As such, inter-prediction can encodean image block in a current frame as a set of motion vectors indicatingan offset from a corresponding block in a reference frame.

Intra-prediction encodes blocks in a common frame. Intra-predictiontakes advantage of the fact that luma and chroma components tend tocluster in a frame. For example, a patch of green in a portion of a treetends to be positioned adjacent to similar patches of green.Intra-prediction employs multiple directional prediction modes (e.g.,thirty-three in HEVC), a planar mode, and a direct current (DC) mode.The directional modes indicate that a current block is similar/the sameas samples of a neighbor block in a corresponding direction. Planar modeindicates that a series of blocks along a row/column (e.g., a plane) canbe interpolated based on neighbor blocks at the edges of the row. Planarmode, in effect, indicates a smooth transition of light/color across arow/column by employing a relatively constant slope in changing values.DC mode is employed for boundary smoothing and indicates that a block issimilar/the same as an average value associated with samples of all theneighbor blocks associated with the angular directions of thedirectional prediction modes. Accordingly, intra-prediction blocks canrepresent image blocks as various relational prediction mode valuesinstead of the actual values. Further, inter-prediction blocks canrepresent image blocks as motion vector values instead of the actualvalues. In either case, the prediction blocks may not exactly representthe image blocks in some cases. Any differences are stored in residualblocks. Transforms may be applied to the residual blocks to furthercompress the file.

At step 107, various filtering techniques may be applied. In HEVC, thefilters are applied according to an in-loop filtering scheme. The blockbased prediction discussed above may result in the creation of blockyimages at the decoder. Further, the block based prediction scheme mayencode a block and then reconstruct the encoded block for later use as areference block. The in-loop filtering scheme iteratively applies noisesuppression filters, de-blocking filters, adaptive loop filters, andsample adaptive offset (SAO) filters to the blocks/frames. These filtersmitigate such blocking artifacts so that the encoded file can beaccurately reconstructed. Further, these filters mitigate artifacts inthe reconstructed reference blocks so that artifacts are less likely tocreate additional artifacts in subsequent blocks that are encoded basedon the reconstructed reference blocks.

Once the video signal has been partitioned, compressed, and filtered,the resulting data is encoded in a bitstream at step 109. The bitstreamincludes the data discussed above as well as any signaling data desiredto support proper video signal reconstruction at the decoder. Forexample, such data may include partition data, prediction data, residualblocks, and various flags providing coding instructions to the decoder.The bitstream may be stored in memory for transmission toward a decoderupon request. The bitstream may also be broadcast and/or multicasttoward a plurality of decoders. The creation of the bitstream is aniterative process. Accordingly, steps 101, 103, 105, 107, and 109 mayoccur continuously and/or simultaneously over many frames and blocks.The order shown in FIG. 1 is presented for clarity and ease ofdiscussion, and is not intended to limit the video coding process to aparticular order.

The decoder receives the bitstream and begins the decoding process atstep 111. Specifically, the decoder employs an entropy decoding schemeto convert the bitstream into corresponding syntax and video data. Thedecoder employs the syntax data from the bitstream to determine thepartitions for the frames at step 111. The partitioning should match theresults of block partitioning at step 103. Entropy encoding/decoding asemployed in step 111 is now described. The encoder makes many choicesduring the compression process, such as selecting block partitioningschemes from several possible choices based on the spatial positioningof values in the input image(s). Signaling the exact choices may employa large number of bins. As used herein, a bin is a binary value that istreated as a variable (e.g., a bit value that may vary depending oncontext). Entropy coding allows the encoder to discard any options thatare clearly not viable for a particular case, leaving a set of allowableoptions. Each allowable option is then assigned a code word. The lengthof the code words is based on the number of allowable options (e.g., onebin for two options, two bins for three to four options, etc.) Theencoder then encodes the code word for the selected option. This schemereduces the size of the code words as the code words are as big asdesired to uniquely indicate a selection from a small sub-set ofallowable options as opposed to uniquely indicating the selection from apotentially large set of all possible options. The decoder then decodesthe selection by determining the set of allowable options in a similarmanner to the encoder. By determining the set of allowable options, thedecoder can read the code word and determine the selection made by theencoder.

At step 113, the decoder performs block decoding. Specifically, thedecoder employs reverse transforms to generate residual blocks. Then thedecoder employs the residual blocks and corresponding prediction blocksto reconstruct the image blocks according to the partitioning. Theprediction blocks may include both intra-prediction blocks andinter-prediction blocks as generated at the encoder at step 105. Thereconstructed image blocks are then positioned into frames of areconstructed video signal according to the partitioning data determinedat step 111. Syntax for step 113 may also be signaled in the bitstreamvia entropy coding as discussed above.

At step 115, filtering is performed on the frames of the reconstructedvideo signal in a manner similar to step 107 at the encoder. Forexample, noise suppression filters, de-blocking filters, adaptive loopfilters, and SAO filters may be applied to the frames to remove blockingartifacts. Once the frames are filtered, the video signal can be outputto a display at step 117 for viewing by an end user.

FIG. 2 is a schematic diagram of an example coding and decoding (codec)system 200 for video coding. Specifically, codec system 200 providesfunctionality to support the implementation of operating method 100.Codec system 200 is generalized to depict components employed in both anencoder and a decoder. Codec system 200 receives and partitions a videosignal as discussed with respect to steps 101 and 103 in operatingmethod 100, which results in a partitioned video signal 201. Codecsystem 200 then compresses the partitioned video signal 201 into a codedbitstream when acting as an encoder as discussed with respect to steps105, 107, and 109 in method 100. When acting as a decoder, codec system200 generates an output video signal from the bitstream as discussedwith respect to steps 111, 113, 115, and 117 in operating method 100.The codec system 200 includes a general coder control component 211, atransform scaling and quantization component 213, an intra-pictureestimation component 215, an intra-picture prediction component 217, amotion compensation component 219, a motion estimation component 221, ascaling and inverse transform component 229, a filter control analysiscomponent 227, an in-loop filters component 225, a decoded picturebuffer component 223, and a header formatting and context adaptivebinary arithmetic coding (CABAC) component 231. Such components arecoupled as shown. In FIG. 2, black lines indicate movement of data to beencoded/decoded while dashed lines indicate movement of control datathat controls the operation of other components. The components of codecsystem 200 may all be present in the encoder. The decoder may include asubset of the components of codec system 200. For example, the decodermay include the intra-picture prediction component 217, the motioncompensation component 219, the scaling and inverse transform component229, the in-loop filters component 225, and the decoded picture buffercomponent 223. These components are now described.

The partitioned video signal 201 is a captured video sequence that hasbeen partitioned into blocks of pixels by a coding tree. A coding treeemploys various split modes to subdivide a block of pixels into smallerblocks of pixels. These blocks can then be further subdivided intosmaller blocks. The blocks may be referred to as nodes on the codingtree. Larger parent nodes are split into smaller child nodes. The numberof times a node is subdivided is referred to as the depth of thenode/coding tree. The divided blocks can be included in coding units(CUs) in some cases. For example, a CU can be a sub-portion of a CTUthat contains a luma block, red difference chroma (Cr) block(s), and ablue difference chroma (Cb) block(s) along with corresponding syntaxinstructions for the CU. The split modes may include a binary tree (BT),triple tree (TT), and a quad tree (QT) employed to partition a node intotwo, three, or four child nodes, respectively, of varying shapesdepending on the split modes employed. The partitioned video signal 201is forwarded to the general coder control component 211, the transformscaling and quantization component 213, the intra-picture estimationcomponent 215, the filter control analysis component 227, and the motionestimation component 221 for compression.

The general coder control component 211 is configured to make decisionsrelated to coding of the images of the video sequence into the bitstreamaccording to application constraints. For example, the general codercontrol component 211 manages optimization of bitrate/bitstream sizeversus reconstruction quality. Such decisions may be made based onstorage space/bandwidth availability and image resolution requests. Thegeneral coder control component 211 also manages buffer utilization inlight of transmission speed to mitigate buffer underrun and overrunissues. To manage these issues, the general coder control component 211manages partitioning, prediction, and filtering by the other components.For example, the general coder control component 211 may dynamicallyincrease compression complexity to increase resolution and increasebandwidth usage or decrease compression complexity to decreaseresolution and bandwidth usage. Hence, the general coder controlcomponent 211 controls the other components of codec system 200 tobalance video signal reconstruction quality with bit rate concerns. Thegeneral coder control component 211 creates control data, which controlsthe operation of the other components. The control data is alsoforwarded to the header formatting and CABAC component 231 to be encodedin the bitstream to signal parameters for decoding at the decoder.

The partitioned video signal 201 is also sent to the motion estimationcomponent 221 and the motion compensation component 219 forinter-prediction. A frame or slice of the partitioned video signal 201may be divided into multiple video blocks. Motion estimation component221 and the motion compensation component 219 perform inter-predictivecoding of the received video block relative to one or more blocks in oneor more reference frames to provide temporal prediction. Codec system200 may perform multiple coding passes, e.g., to select an appropriatecoding mode for each block of video data.

Motion estimation component 221 and motion compensation component 219may be highly integrated, but are illustrated separately for conceptualpurposes. Motion estimation, performed by motion estimation component221, is the process of generating motion vectors, which estimate motionfor video blocks. A motion vector, for example, may indicate thedisplacement of a coded object relative to a predictive block. Apredictive block is a block that is found to closely match the block tobe coded, in terms of pixel difference. A predictive block may also bereferred to as a reference block. Such pixel difference may bedetermined by sum of absolute difference (SAD), sum of square difference(SSD), or other difference metrics. HEVC employs several coded objectsincluding a CTU, coding tree blocks (CTBs), and CUs. For example, a CTUcan be divided into CTBs, which can then be divided into CBs forinclusion in CUs. A CU can be encoded as a prediction unit containingprediction data and/or a transform unit (TU) containing transformedresidual data for the CU. The motion estimation component 221 generatesmotion vectors, prediction units, and TUs by using a rate-distortionanalysis as part of a rate distortion optimization process. For example,the motion estimation component 221 may determine multiple referenceblocks, multiple motion vectors, etc. for a current block/frame, and mayselect the reference blocks, motion vectors, etc. having the bestrate-distortion characteristics. The best rate-distortioncharacteristics balance both quality of video reconstruction (e.g.,amount of data loss by compression) with coding efficiency (e.g., sizeof the final encoding).

In some examples, codec system 200 may calculate values for sub-integerpixel positions of reference pictures stored in decoded picture buffercomponent 223. For example, video codec system 200 may interpolatevalues of one-quarter pixel positions, one-eighth pixel positions, orother fractional pixel positions of the reference picture. Therefore,motion estimation component 221 may perform a motion search relative tothe full pixel positions and fractional pixel positions and output amotion vector with fractional pixel precision. The motion estimationcomponent 221 calculates a motion vector for a prediction unit of avideo block in an inter-coded slice by comparing the position of theprediction unit to the position of a predictive block of a referencepicture. Motion estimation component 221 outputs the calculated motionvector as motion data to header formatting and CABAC component 231 forencoding and motion to the motion compensation component 219.

Motion compensation, performed by motion compensation component 219, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation component 221. Again, motionestimation component 221 and motion compensation component 219 may befunctionally integrated, in some examples. Upon receiving the motionvector for the prediction unit of the current video block, motioncompensation component 219 may locate the predictive block to which themotion vector points. A residual video block is then formed bysubtracting pixel values of the predictive block from the pixel valuesof the current video block being coded, forming pixel difference values.In general, motion estimation component 221 performs motion estimationrelative to luma components, and motion compensation component 219 usesmotion vectors calculated based on the luma components for both chromacomponents and luma components. The predictive block and residual blockare forwarded to transform scaling and quantization component 213.

The partitioned video signal 201 is also sent to intra-pictureestimation component 215 and intra-picture prediction component 217. Aswith motion estimation component 221 and motion compensation component219, intra-picture estimation component 215 and intra-picture predictioncomponent 217 may be highly integrated, but are illustrated separatelyfor conceptual purposes. The intra-picture estimation component 215 andintra-picture prediction component 217 intra-predict a current blockrelative to blocks in a current frame, as an alternative to theinter-prediction performed by motion estimation component 221 and motioncompensation component 219 between frames, as described above. Inparticular, the intra-picture estimation component 215 determines anintra-prediction mode to use to encode a current block. In someexamples, intra-picture estimation component 215 selects an appropriateintra-prediction mode to encode a current block from multiple testedintra-prediction modes. The selected intra-prediction modes are thenforwarded to the header formatting and CABAC component 231 for encoding.

For example, the intra-picture estimation component 215 calculatesrate-distortion values using a rate-distortion analysis for the varioustested intra-prediction modes, and selects the intra-prediction modehaving the best rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original unencoded block thatwas encoded to produce the encoded block, as well as a bitrate (e.g., anumber of bits) used to produce the encoded block. The intra-pictureestimation component 215 calculates ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block. In addition,intra-picture estimation component 215 may be configured to code depthblocks of a depth map using a depth modeling mode (DMM) based onrate-distortion optimization (RDO).

The intra-picture prediction component 217 may generate a residual blockfrom the predictive block based on the selected intra-prediction modesdetermined by intra-picture estimation component 215 when implemented onan encoder or read the residual block from the bitstream whenimplemented on a decoder. The residual block includes the difference invalues between the predictive block and the original block, representedas a matrix. The residual block is then forwarded to the transformscaling and quantization component 213. The intra-picture estimationcomponent 215 and the intra-picture prediction component 217 may operateon both luma and chroma components.

The transform scaling and quantization component 213 is configured tofurther compress the residual block. The transform scaling andquantization component 213 applies a transform, such as a discretecosine transform (DCT), a discrete sine transform (DST), or aconceptually similar transform, to the residual block, producing a videoblock comprising residual transform coefficient values. Wavelettransforms, integer transforms, sub-band transforms or other types oftransforms could also be used. The transform may convert the residualinformation from a pixel value domain to a transform domain, such as afrequency domain. The transform scaling and quantization component 213is also configured to scale the transformed residual information, forexample based on frequency. Such scaling involves applying a scalefactor to the residual information so that different frequencyinformation is quantized at different granularities, which may affectfinal visual quality of the reconstructed video. The transform scalingand quantization component 213 is also configured to quantize thetransform coefficients to further reduce bit rate. The quantizationprocess may reduce the bit depth associated with some or all of thecoefficients. The degree of quantization may be modified by adjusting aquantization parameter. In some examples, the transform scaling andquantization component 213 may then perform a scan of the matrixincluding the quantized transform coefficients. The quantized transformcoefficients are forwarded to the header formatting and CABAC component231 to be encoded in the bitstream.

The scaling and inverse transform component 229 applies a reverseoperation of the transform scaling and quantization component 213 tosupport motion estimation. The scaling and inverse transform component229 applies inverse scaling, transformation, and/or quantization toreconstruct the residual block in the pixel domain, e.g., for later useas a reference block which may become a predictive block for anothercurrent block. The motion estimation component 221 and/or motioncompensation component 219 may calculate a reference block by adding theresidual block back to a corresponding predictive block for use inmotion estimation of a later block/frame. Filters are applied to thereconstructed reference blocks to mitigate artifacts created duringscaling, quantization, and transform. Such artifacts could otherwisecause inaccurate prediction (and create additional artifacts) whensubsequent blocks are predicted.

The filter control analysis component 227 and the in-loop filterscomponent 225 apply the filters to the residual blocks and/or toreconstructed image blocks. For example, the transformed residual blockfrom the scaling and inverse transform component 229 may be combinedwith a corresponding prediction block from intra-picture predictioncomponent 217 and/or motion compensation component 219 to reconstructthe original image block. The filters may then be applied to thereconstructed image block. In some examples, the filters may instead beapplied to the residual blocks. As with other components in FIG. 2, thefilter control analysis component 227 and the in-loop filters component225 are highly integrated and may be implemented together, but aredepicted separately for conceptual purposes. Filters applied to thereconstructed reference blocks are applied to particular spatial regionsand include multiple parameters to adjust how such filters are applied.The filter control analysis component 227 analyzes the reconstructedreference blocks to determine where such filters should be applied andsets corresponding parameters. Such data is forwarded to the headerformatting and CABAC component 231 as filter control data for encoding.The in-loop filters component 225 applies such filters based on thefilter control data. The filters may include a deblocking filter, anoise suppression filter, a SAO filter, and an adaptive loop filter.Such filters may be applied in the spatial/pixel domain (e.g., on areconstructed pixel block) or in the frequency domain, depending on theexample.

When operating as an encoder, the filtered reconstructed image block,residual block, and/or prediction block are stored in the decodedpicture buffer component 223 for later use in motion estimation asdiscussed above. When operating as a decoder, the decoded picture buffercomponent 223 stores and forwards the reconstructed and filtered blockstoward a display as part of an output video signal. The decoded picturebuffer component 223 may be any memory device capable of storingprediction blocks, residual blocks, and/or reconstructed image blocks.

The header formatting and CABAC component 231 receives the data from thevarious components of codec system 200 and encodes such data into acoded bitstream for transmission toward a decoder. Specifically, theheader formatting and CABAC component 231 generates various headers toencode control data, such as general control data and filter controldata. Further, prediction data, including intra-prediction and motiondata, as well as residual data in the form of quantized transformcoefficient data are all encoded in the bitstream. The final bitstreamincludes all information desired by the decoder to reconstruct theoriginal partitioned video signal 201. Such information may also includeintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks,indications of most probable intra-prediction modes, an indication ofpartition information, etc. Such data may be encoded by employingentropy coding. For example, the information may be encoded by employingcontext adaptive variable length coding (CAVLC), CABAC, syntax-basedcontext-adaptive binary arithmetic coding (SBAC), probability intervalpartitioning entropy (PIPE) coding, or another entropy coding technique.Following the entropy coding, the coded bitstream may be transmitted toanother device (e.g., a video decoder) or archived for latertransmission or retrieval.

FIG. 3 is a block diagram illustrating an example video encoder 300.Video encoder 300 may be employed to implement the encoding functions ofcodec system 200 and/or implement steps 101, 103, 105, 107, and/or 109of operating method 100. Encoder 300 partitions an input video signal,resulting in a partitioned video signal 301, which is substantiallysimilar to the partitioned video signal 201. The partitioned videosignal 301 is then compressed and encoded into a bitstream by componentsof encoder 300.

Specifically, the partitioned video signal 301 is forwarded to anintra-picture prediction component 317 for intra-prediction. Theintra-picture prediction component 317 may be substantially similar tointra-picture estimation component 215 and intra-picture predictioncomponent 217. The partitioned video signal 301 is also forwarded to amotion compensation component 321 for inter-prediction based onreference blocks in a decoded picture buffer component 323. The motioncompensation component 321 may be substantially similar to motionestimation component 221 and motion compensation component 219. Theprediction blocks and residual blocks from the intra-picture predictioncomponent 317 and the motion compensation component 321 are forwarded toa transform and quantization component 313 for transform andquantization of the residual blocks. The transform and quantizationcomponent 313 may be substantially similar to the transform scaling andquantization component 213. The transformed and quantized residualblocks and the corresponding prediction blocks (along with associatedcontrol data) are forwarded to an entropy coding component 331 forcoding into a bitstream. The entropy coding component 331 may besubstantially similar to the header formatting and CABAC component 231.

The transformed and quantized residual blocks and/or the correspondingprediction blocks are also forwarded from the transform and quantizationcomponent 313 to an inverse transform and quantization component 329 forreconstruction into reference blocks for use by the motion compensationcomponent 321. The inverse transform and quantization component 329 maybe substantially similar to the scaling and inverse transform component229. In-loop filters in an in-loop filters component 325 are alsoapplied to the residual blocks and/or reconstructed reference blocks,depending on the example. The in-loop filters component 325 may besubstantially similar to the filter control analysis component 227 andthe in-loop filters component 225. The in-loop filters component 325 mayinclude multiple filters as discussed with respect to in-loop filterscomponent 225. The filtered blocks are then stored in a decoded picturebuffer component 323 for use as reference blocks by the motioncompensation component 321. The decoded picture buffer component 323 maybe substantially similar to the decoded picture buffer component 223.

FIG. 4 is a block diagram illustrating an example video decoder 400.Video decoder 400 may be employed to implement the decoding functions ofcodec system 200 and/or implement steps 111, 113, 115, and/or 117 ofoperating method 100. Decoder 400 receives a bitstream, for example froman encoder 300, and generates a reconstructed output video signal basedon the bitstream for display to an end user.

The bitstream is received by an entropy decoding component 433. Theentropy decoding component 433 is configured to implement an entropydecoding scheme, such as CAVLC, CABAC, SBAC, PIPE coding, or otherentropy coding techniques. For example, the entropy decoding component433 may employ header information to provide a context to interpretadditional data encoded as codewords in the bitstream. The decodedinformation includes any desired information to decode the video signal,such as general control data, filter control data, partitioninformation, motion data, prediction data, and quantized transformcoefficients from residual blocks. The quantized transform coefficientsare forwarded to an inverse transform and quantization component 429 forreconstruction into residual blocks. The inverse transform andquantization component 429 may be similar to inverse transform andquantization component 329.

The reconstructed residual blocks and/or prediction blocks are forwardedto intra-picture prediction component 417 for reconstruction into imageblocks based on intra-prediction operations. The intra-pictureprediction component 417 may be similar to intra-picture estimationcomponent 215 and an intra-picture prediction component 217.Specifically, the intra-picture prediction component 417 employsprediction modes to locate a reference block in the frame and applies aresidual block to the result to reconstruct intra-predicted imageblocks. The reconstructed intra-predicted image blocks and/or theresidual blocks and corresponding inter-prediction data are forwarded toa decoded picture buffer component 423 via an in-loop filters component425, which may be substantially similar to decoded picture buffercomponent 223 and in-loop filters component 225, respectively. Thein-loop filters component 425 filters the reconstructed image blocks,residual blocks and/or prediction blocks, and such information is storedin the decoded picture buffer component 423. Reconstructed image blocksfrom decoded picture buffer component 423 are forwarded to a motioncompensation component 421 for inter-prediction. The motion compensationcomponent 421 may be substantially similar to motion estimationcomponent 221 and/or motion compensation component 219. Specifically,the motion compensation component 421 employs motion vectors from areference block to generate a prediction block and applies a residualblock to the result to reconstruct an image block. The resultingreconstructed blocks may also be forwarded via the in-loop filterscomponent 425 to the decoded picture buffer component 423. The decodedpicture buffer component 423 continues to store additional reconstructedimage blocks, which can be reconstructed into frames via the partitioninformation. Such frames may also be placed in a sequence. The sequenceis output toward a display as a reconstructed output video signal.

FIG. 5 is a schematic diagram illustrating an example HRD 500. A HRD 500may be employed in an encoder, such as codec system 200 and/or encoder300. The HRD 500 may check the bitstream created at step 109 of method100 before the bitstream is forwarded to a decoder, such as decoder 400.In some examples, the bitstream may be continuously forwarded throughthe HRD 500 as the bitstream is encoded. In the event that a portion ofthe bitstream fails to conform to associated constraints, the HRD 500can indicate such failure to an encoder to cause the encoder tore-encode the corresponding section of the bitstream with differentmechanisms.

The HRD 500 includes a hypothetical stream scheduler (HSS) 541. A HSS541 is a component configured to perform a hypothetical deliverymechanism. The hypothetical delivery mechanism is used for checking theconformance of a bitstream or a decoder with regards to the timing anddata flow of a bitstream 551 input into the HRD 500. For example, theHSS 541 may receive a bitstream 551 output from an encoder and managethe conformance testing process on the bitstream 551. In a particularexample, the HSS 541 can control the rate that coded pictures movethrough the HRD 500 and verify that the bitstream 551 does not containnon-conforming data.

The HSS 541 may forward the bitstream 551 to a CPB 543 at a predefinedrate. The HRD 500 may manage data in decoding units (DU) 553. A DU 553is an Access Unit (AU) or a sub-set of an AU and associated non-videocoding layer (VCL) network abstraction layer (NAL) units. Specifically,an AU contains one or more pictures associated with an output time. Forexample, an AU may contain a single picture in a single layer bitstream,and may contain a picture for each layer in a multi-layer bitstream.Each picture of an AU may be divided into slices that are each includedin a corresponding VCL NAL unit. Hence, a DU 553 may contain one or morepictures, one or more slices of a picture, or combinations thereof.Also, parameters used to decode the AU, pictures, and/or slices can beincluded in non-VCL NAL units. As such, the DU 553 contains non-VCL NALunits that contain data needed to support decoding the VCL NAL units inthe DU 553. The CPB 543 is a first-in first-out buffer in the HRD 500.The CPB 543 contains DUs 553 including video data in decoding order. TheCPB 543 stores the video data for use during bitstream conformanceverification.

The CPB 543 forwards the DUs 553 to a decoding process component 545.The decoding process component 545 is a component that conforms to theVVC standard. For example, the decoding process component 545 mayemulate a decoder 400 employed by an end user. The decoding processcomponent 545 decodes the DUs 553 at a rate that can be achieved by anexample end user decoder. If the decoding process component 545 cannotdecode the DUs 553 fast enough to prevent an overflow of the CPB 543,then the bitstream 551 does not conform to the standard and should bere-encoded.

The decoding process component 545 decodes the DUs 553, which createsdecoded DUs 555. A decoded DU 555 contains a decoded picture. Thedecoded DUs 555 are forwarded to a DPB 547. The DPB 547 may besubstantially similar to a decoded picture buffer component 223, 323,and/or 423. To support inter-prediction, pictures that are marked foruse as reference pictures 556 that are obtained from the decoded DUs 555are returned to the decoding process component 545 to support furtherdecoding. The DPB 547 outputs the decoded video sequence as a series ofpictures 557. The pictures 557 are reconstructed pictures that generallymirror pictures encoded into the bitstream 551 by the encoder.

The pictures 557 are forwarded to an output cropping component 549. Theoutput cropping component 549 is configured to apply a conformancecropping window to the pictures 557. This results in output croppedpictures 559. An output cropped picture 559 is a completelyreconstructed picture. Accordingly, the output cropped picture 559mimics what an end user would see upon decoding the bitstream 551. Assuch, the encoder can review the output cropped pictures 559 to ensurethe encoding is satisfactory.

The HRD 500 is initialized based on HRD parameters in the bitstream 551.For example, the HRD 500 may read HRD parameters from a VPS, a SPS,and/or SEI messages. The HRD 500 may then perform conformance testingoperations on the bitstream 551 based on the information in such HRDparameters. As a specific example, the HRD 500 may determine one or moreCPB delivery schedules from the HRD parameters. A delivery schedulespecifies timing for delivery of video data to and/or from a memorylocation, such as a CPB and/or a DPB. Hence, a CPB delivery schedulespecifies timing for delivery of AUs, DUs 553, and/or pictures, to/fromthe CPB 543. It should be noted that the HRD 500 may employ DPB deliveryschedules for the DPB 547 that are similar to the CPB deliveryschedules.

Video may be coded into different layers and/or OLSs for use by decoderswith varying levels of hardware capabilities as well for varying networkconditions. The CPB delivery schedules are selected to reflect theseissues. Accordingly, higher layer sub-bitstreams are designated foroptimal hardware and network conditions and hence higher layers mayreceive one or more CPB delivery schedules that employ a large amount ofmemory in the CPB 543 and short delays for transfers of the DUs 553toward the DPB 547. Likewise, lower layer sub-bitstreams are designatedfor limited decoder hardware capabilities and/or poor networkconditions. Hence, lower layers may receive one or more CPB deliveryschedules that employ a small amount of memory in the CPB 543 and longerdelays for transfers of the DUs 553 toward the DPB 547. The OLSs,layers, sublayers, or combinations thereof can then be tested accordingto the corresponding delivery schedule to ensure that the resultingsub-bitstream can be correctly decoded under the conditions that areexpected for the sub-bitstream. Accordingly, the HRD parameters in thebitstream 551 can indicate the CPB delivery schedules as well as includesufficient data to allow the HRD 500 to determine the CPB deliveryschedules and correlate the CPB delivery schedules to the correspondingOLSs, layers, and/or sublayers.

FIG. 6 is a schematic diagram illustrating an example multi-layer videosequence 600. The multi-layer video sequence 600 may be encoded by anencoder, such as codec system 200 and/or encoder 300 and decoded by adecoder, such as codec system 200 and/or decoder 400, for exampleaccording to method 100. Further, the multi-layer video sequence 600 canbe checked for standard conformance by a HRD, such as HRD 500. Themulti-layer video sequence 600 is included to depict an exampleapplication for layers in a coded video sequence. A multi-layer videosequence 600 is any video sequence that employs a plurality of layers,such as layer N 631 and layer N+1 632.

In an example, the multi-layer video sequence 600 may employ inter-layerprediction 621. Inter-layer prediction 621 is applied between pictures611, 612, 613, and 614 and pictures 615, 616, 617, and 618 in differentlayers. In the example shown, pictures 611, 612, 613, and 614 are partof layer N+1 632 and pictures 615, 616, 617, and 618 are part of layer N631. A layer, such as layer N 631 and/or layer N+1 632, is a group ofpictures that are all associated with a similar value of acharacteristic, such as a similar size, quality, resolution, signal tonoise ratio, capability, etc. A layer may be defined formally as a setof VCL NAL units that share the same layer ID and associated non-VCL NALunits. A VCL NAL unit is a NAL unit coded to contain video data, such asa coded slice of a picture. A non-VCL NAL unit is a NAL unit thatcontains non-video data such as syntax and/or parameters that supportdecoding the video data, performance of conformance checking, or otheroperations.

In the example shown, layer N+1 632 is associated with a larger imagesize than layer N 631. Accordingly, pictures 611, 612, 613, and 614 inlayer N+1 632 have a larger picture size (e.g., larger height and widthand hence more samples) than pictures 615, 616, 617, and 618 in layer N631 in this example. However, such pictures can be separated betweenlayer N+1 632 and layer N 631 by other characteristics. While only twolayers, layer N+1 632 and layer N 631, are shown, a set of pictures canbe separated into any number of layers based on associatedcharacteristics. Layer N+1 632 and layer N 631 may also be denoted by alayer ID. A layer ID is an item of data that is associated with apicture and denotes the picture is part of an indicated layer.Accordingly, each picture 611-618 may be associated with a correspondinglayer ID to indicate which layer N+1 632 or layer N 631 includes thecorresponding picture. For example, a layer ID may include a NAL unitheader layer identifier (nuh_layer_id), which is a syntax element thatspecifies an identifier of a layer that includes a NAL unit (e.g., thatinclude slices and/or parameters of the pictures in a layer). A layerassociated with a lower quality/smaller image size/smaller bitstreamsize, such as layer N 631, is generally assigned a lower layer ID and isreferred to as a lower layer. Further, a layer associated with a higherquality/larger image size/larger bitstream size, such as layer N+1 632,is generally assigned a higher layer ID and is referred to as a higherlayer.

Pictures 611-618 in different layers 631-632 are configured to bedisplayed in the alternative. As a specific example, a decoder maydecode and display picture 615 at a current display time if a smallerpicture is desired or the decoder may decode and display picture 611 atthe current display time if a larger picture is desired. As such,pictures 611-614 at higher layer N+1 632 contain substantially the sameimage data as corresponding pictures 615-618 at lower layer N 631(notwithstanding the difference in picture size). Specifically, picture611 contains substantially the same image data as picture 615, picture612 contains substantially the same image data as picture 616, etc.

Pictures 611-618 can be coded by reference to other pictures 611-618 inthe same layer N 631 or N+1 632. Coding a picture in reference toanother picture in the same layer results in inter-prediction 623.Inter-prediction 623 is depicted by solid line arrows. For example,picture 613 may be coded by employing inter-prediction 623 using one ortwo of pictures 611, 612, and/or 614 in layer N+1 632 as a reference,where one picture is referenced for unidirectional inter-predictionand/or two pictures are referenced for bidirectional inter-prediction.Further, picture 617 may be coded by employing inter-prediction 623using one or two of pictures 615, 616, and/or 618 in layer N 631 as areference, where one picture is referenced for unidirectionalinter-prediction and/or two pictures are referenced for bidirectionalinter-prediction. When a picture is used as a reference for anotherpicture in the same layer when performing inter-prediction 623, thepicture may be referred to as a reference picture. For example, picture612 may be a reference picture used to code picture 613 according tointer-prediction 623. Inter-prediction 623 can also be referred to asintra-layer prediction in a multi-layer context. As such,inter-prediction 623 is a mechanism of coding samples of a currentpicture by reference to indicated samples in a reference picture that isdifferent from the current picture where the reference picture and thecurrent picture are in the same layer.

Pictures 611-618 can also be coded by reference to other pictures611-618 in different layers. This process is known as inter-layerprediction 621, and is depicted by dashed arrows. Inter-layer prediction621 is a mechanism of coding samples of a current picture by referenceto indicated samples in a reference picture where the current pictureand the reference picture are in different layers and hence havedifferent layer IDs. For example, a picture in a lower layer N 631 canbe used as a reference picture to code a corresponding picture at ahigher layer N+1 632. As a specific example, picture 611 can be coded byreference to picture 615 according to inter-layer prediction 621. Insuch a case, the picture 615 is used as an inter-layer referencepicture. An inter-layer reference picture is a reference picture usedfor inter-layer prediction 621. In most cases, inter-layer prediction621 is constrained such that a current picture, such as picture 611, canonly use inter-layer reference picture(s) that are included in the sameAU 627 and that are at a lower layer, such as picture 615. When multiplelayers (e.g., more than two) are available, inter-layer prediction 621can encode/decode a current picture based on multiple inter-layerreference picture(s) at lower levels than the current picture.

A video encoder can employ a multi-layer video sequence 600 to encodepictures 611-618 via many different combinations and/or permutations ofinter-prediction 623 and inter-layer prediction 621. For example,picture 615 may be coded according to intra-prediction. Pictures 616-618can then be coded according to inter-prediction 623 by using picture 615as a reference picture. Further, picture 611 may be coded according tointer-layer prediction 621 by using picture 615 as an inter-layerreference picture. Pictures 612-614 can then be coded according tointer-prediction 623 by using picture 611 as a reference picture. Assuch, a reference picture can serve as both a single layer referencepicture and an inter-layer reference picture for different codingmechanisms. By coding higher layer N+1 632 pictures based on lower layerN 631 pictures, the higher layer N+1 632 can avoid employingintra-prediction, which has much lower coding efficiency thaninter-prediction 623 and inter-layer prediction 621. As such, the poorcoding efficiency of intra-prediction can be limited to thesmallest/lowest quality pictures, and hence limited to coding thesmallest amount of video data. The pictures used as reference picturesand/or inter-layer reference pictures can be indicated in entries ofreference picture list(s) contained in a reference picture liststructure.

The pictures 611-618 may also be included in access units (AUs) 627. AnAU 627 is a set of coded pictures that are included in different layersand are associated with the same output time during decoding.Accordingly, coded pictures in the same AU 627 are scheduled for outputfrom a DPB at a decoder at the same time. For example, pictures 614 and618 are in the same AU 627. Pictures 613 and 617 are in a different AU627 from pictures 614 and 618. Pictures 614 and 618 in the same AU 627may be displayed in the alternative. For example, picture 618 may bedisplayed when a small picture size is desired and picture 614 may bedisplayed when a large picture size is desired. When the large picturesize is desired, picture 614 is output and picture 618 is used only forinterlayer prediction 621. In this case, picture 618 is discardedwithout being output once interlayer prediction 621 is complete.

An AU 627 can be further divided into one or more picture units (PUs)628. A PU 628 is a subset of an AU 627 that contains a single codedpicture. A PU 628 can be formally defined as a set of NAL units that areassociated with each other according to a specified classification rule,are consecutive in decoding order, and contain exactly one codedpicture. It should be noted that a PU 628 can be referred to as adecoding unit (DU) when discussed in terms of a HRD and/or associatedconformance tests.

It should also be noted that pictures 611-618, and hence AUs 627 and PUs628, are each associated with a temporal identifier (TemporalId) 629. ATemporalId 629 is a derived identifier that indicates the relativeposition of a NAL unit in a video sequence. Pictures and/or PUs 628 inthe same AU 627 are associated with the same value of TemporalId 629.For example, a first AU 627 in a sequence may include a TemporalId 629of zero, with subsequent AUs 627 including consecutively increasingTemporalIds 629. Non-VCL NAL units may also be associated withTemporalIds 629. For example, a parameter set may be included in an AU627 and may be associated with one or more pictures in the AU 627. Insuch a case, the TemporalId 629 of the parameter set may be less than orequal to the TemporalId 629 of the AU 627.

FIG. 7 is a schematic diagram illustrating an example bitstream 700. Forexample, the bitstream 700 can be generated by a codec system 200 and/oran encoder 300 for decoding by a codec system 200 and/or a decoder 400according to method 100. Further, the bitstream 700 may include amulti-layer video sequence 600. In addition, the bitstream 700 mayinclude various parameters to control the operation of a HRD, such asHRD 500. Based on such parameters, the HRD can check the bitstream 700for conformance with standards prior to transmission toward a decoderfor decoding.

The bitstream 700 includes a VPS 711, one or more SPSs 713, a pluralityof picture parameter sets (PPSs) 715, a plurality of adaptationparameter sets (APSs) 716, a plurality of picture headers 718, aplurality of slice headers 717, image data 720, and SEI messages 719. AVPS 711 contains data related to the entire bitstream 700. For example,the VPS 711 may contain data related OLSs, layers, and/or sublayers usedin the bitstream 700. An SPS 713 contains sequence data common to allpictures in a coded video sequence contained in the bitstream 700. Forexample, each layer may contain one or more coded video sequences, andeach coded video sequence may reference a SPS 713 for correspondingparameters. The parameters in a SPS 713 can include picture sizing, bitdepth, coding tool parameters, bit rate restrictions, etc. It should benoted that, while each sequence refers to a SPS 713, a single SPS 713can contain data for multiple sequences in some examples. The PPS 715contains parameters that apply to an entire picture. Hence, each picturein the video sequence may refer to a PPS 715. It should be noted that,while each picture refers to a PPS 715, a single PPS 715 can containdata for multiple pictures in some examples. For example, multiplesimilar pictures may be coded according to similar parameters. In such acase, a single PPS 715 may contain data for such similar pictures. ThePPS 715 can indicate coding tools available for slices in correspondingpictures, quantization parameters, offsets, etc.

An APS 716 is syntax structure containing syntax elements/parametersthat apply to one or more slices 727 in one or more pictures 725. Suchcorrelations can be determined based on syntax elements found in sliceheaders 717 associated with the slices 727. For example, an APS 716 mayapply to at least one, but less than all, slices 727 in a first picture721, to at least one, but less than all, slices 727 in a second picture725, etc. An APS 716 can be separated into multiple types based on theparameters contained in the APS 716. Such types may include adaptiveloop filter (ALF) APS, luma mapping with chroma scaling (LMCS) APS, andscaling list (Scaling) APS. An ALF is an adaptive block based filterthat includes a transfer function controlled by variable parameters andemploys feedback from a feedback loop to refine the transfer function.Further, the ALF is employed to correct coding artifacts (e.g., errors)that occur as a result of block based coding, such as blurring andringing artifacts. As such, ALF parameters included in an ALF APS mayinclude parameters selected by the encoder to cause an ALF to removeblock based coding artifacts during decoding at the decoder. LMCS is aprocess that is applied as part of the decoding process that maps lumasamples to particular values and in some cases also applies a scalingoperation to the values of chroma samples. The LMCS tool may reshapesluma components based on mappings to corresponding chroma components inorder to reduce rate distortion. As such, a LMCS APS includes parametersselected by the encoder to cause a LMCS tool to reshape luma components.A scaling list APS contains coding tool parameters associated withquantization matrices used by specified filters. As such, an APS 716 maycontain parameters used to apply various filters to coded slices 727during conformance testing at a HRD and/or upon decoding at a decoder.

A picture header 718 is a syntax structure containing syntax elementsthat apply to all slices 727 of a coded picture 725. For example, apicture header 718 may contain picture order count information,reference picture data, data relating in intra-random access point(IRAP) pictures, data related to filter application for a picture 725,etc. A PU may contain exactly one picture header 718 and exactly onepicture 725. As such, the bitstream 700 may include exactly one pictureheader 718 per picture 725. A slice header 717 contains parameters thatare specific to each slice 727 in a picture 725. Hence, there may be oneslice header 717 per slice 727 in the video sequence. The slice header717 may contain slice type information, filtering information,prediction weights, tile entry points, deblocking parameters, etc. Insome instances, syntax elements may be the same for all slices 727 in apicture 725. In order to reduce redundancy, the picture header 718 andslice header 717 may share certain types of information. For example,certain parameters (e.g., filtering parameters) may be included in thepicture header 718 when they apply to an entire picture 725 or includedin a slice header 717 when they apply to a group of slices 727 that area subset of the entire picture 725.

The image data 720 contains video data encoded according tointer-prediction and/or intra-prediction as well as correspondingtransformed and quantized residual data. For example, the image data 720may include layers 723, pictures 725, and/or slices 727. A layer 723 isa set of VCL NAL units 745 that share a specified characteristic (e.g.,a common resolution, frame rate, image size, etc.) as indicated by alayer ID, such as a nuh_layer_id, and associated non-VCL NAL units 741.For example, a layer 723 may include a set of pictures 725 that sharethe same nuh_layer_id. A layer 723 may be substantially similar tolayers 631 and/or 632. A nuh_layer_id is a syntax element that specifiesan identifier of a layer 723 that includes at least one NAL unit. Forexample, the lowest quality layer 723, known as a base layer, mayinclude the lowest value of nuh_layer_id with increasing values ofnuh_layer_id for layers 723 of higher quality. Hence, a lower layer is alayer 723 with a smaller value of nuh_layer_id and a higher layer is alayer 723 with a larger value of nuh_layer_id.

A picture 725 is an array of luma samples and/or an array of chromasamples that create a frame or a field thereof. For example, a picture725 is a coded image that may be output for display or used to supportcoding of other picture(s) 725 for output. A picture 725 contains one ormore slices 727. A slice 727 may be defined as an integer number ofcomplete tiles or an integer number of consecutive complete coding treeunit (CTU) rows (e.g., within a tile) of a picture 725 that areexclusively contained in a single NAL unit. The slices 727 are furtherdivided into CTUs and/or coding tree blocks (CTBs). A CTU is a group ofsamples of a predefined size that can be partitioned by a coding tree. ACTB is a subset of a CTU and contains luma components or chromacomponents of the CTU. The CTUs/CTBs are further divided into codingblocks based on coding trees. The coding blocks can then beencoded/decoded according to prediction mechanisms.

A SEI message 719 is a syntax structure with specified semantics thatconveys information that is not needed by the decoding process in orderto determine the values of the samples in decoded pictures. For example,the SEI messages 719 may contain data to support HRD processes or othersupporting data that is not directly relevant to decoding the bitstream700 at a decoder. A set of SEI messages 719 may be implemented as ascalable nesting SEI message. The scalable nesting SEI message providesa mechanism to associate SEI messages 719 with specific layers 723. Ascalable nesting SEI message is a message that contains a plurality ofscalable-nested SEI messages. A scalable-nested SEI message is an SEImessage 719 that correspond to one or more OLSs or one or more layers723. An OLS is a set of layers 723 where at least one of the layers 723is an output layer. Accordingly, a scalable nesting SEI message can besaid to include a set of scalable-nested SEI messages or said to includea set of SEI messages 719, depending on context. Further, a scalablenesting SEI message contains a set of scalable-nested SEI messages ofthe same type. SEI messages 719 may include a BP SEI message thatcontains HRD parameters for initializing an HRD to manage a CPB fortesting corresponding OLSs and/or layers 723. SEI messages 719 may alsoinclude a PT SEI message that contains HRD parameters for managingdelivery information for AUs at the CPB and/or the DPB for testingcorresponding OLSs and/or layers 723. SEI messages 719 may also includea DUI SEI message that contains HRD parameters for managing deliveryinformation for DUs at the CPB and/or the DPB for testing correspondingOLSs and/or layers 723.

A bitstream 700 can be coded as a sequence of NAL units. A NAL unit is acontainer for video data and/or supporting syntax. ANAL unit can be aVCL NAL unit 745 or a non-VCL NAL unit 741. A VCL NAL unit 745 is a NALunit coded to contain video data. Specifically, a VCL NAL unit 745contains a slice 727 and an associated slice header 717. A non-VCL NALunit 741 is a NAL unit that contains non-video data such as syntaxand/or parameters that support decoding the video data, performance ofconformance checking, or other operations. Non-VCL NAL units 741 mayinclude a VPS NAL unit, a SPS NAL unit, a PPS NAL unit, an APS NAL unit,picture header (PH) NAL unit, and an SEI NAL unit, which contain a VPS711, a SPS 713, a PPS 715, a APS 716, a picture header 718, and a SEImessage 719, respectively. It should be noted that the preceding list ofNAL units is exemplary and not exhaustive.

Each NAL unit is associated with a NAL unit header temporal identifierplus one (nuh_temporal_id_plus1) 731. The nuh_temporal_id_plus1 731 is asignaled identifier that indicates the relative position of acorresponding NAL unit in a video sequence. A decoder and/or a HRD candetermine a TemporalId for the corresponding NAL unit based on the valueof nuh_temporal_id_plus1 731. Specifically, the nuh_temporal_id_plus1731 is signaled in a header of the NAL unit. The TemporalId for the NALunit can be determined by the decoder/HRD by subtracting one from thevalue of nuh_temporal_id_plus1 731. As such, the value ofnuh_temporal_id_plus1 731 should not be set to zero as this would resultin a TemporalId with a negative value.

Further, SEI messages 719 can be employed as prefix SEI messages and/orsuffix SEI messages. A prefix SEI message is a SEI message 719 thatapplies to one or more subsequent NAL units. A suffix SEI message is aSEI message 719 that applies to one or more preceding NAL units. Aprefix SEI message is included in a prefix SEI NAL unit type(PREFIX_SEI_NUT) 742 and a suffix SEI message is included in a suffixSEI NAL unit type (SUFFIX_SEI_NUT) 743. A PREFIX_SEI_NUT 742 is anon-VCL NAL unit with a type value set to indicate the non-VCL NAL unitcontains a prefix SEI message. A SUFFIX_SEI_NUT 743 is a non-VCL NALunit with a type value set to indicate the non-VCL NAL unit contains asuffix SEI message.

As noted above, the SEI messages 719 may contain parameters used by aHRD operating at an encoder to check a bitstream for conformance withstandards. The SEI messages 719 may be related to varying pictures 725and/or varying combinations of layers 723. Accordingly, ensuring thatthe proper SEI message 719 is associated with the proper pictures 725and/or layers 723 can become challenging in complex multi-layerbitstreams. Further, a prefix SEI message should be included in thebitstream 700 prior to the first NAL unit associated with the prefix SEImessage, while a suffix SEI message should be included in the bitstream700 immediately after the first NAL unit associated with the suffix SEImessage. In the event that an SEI message 719 is not positionedcorrectly in the bitstream 700 and/or is not associated with the correctlayer 723 and/or picture 725, the HRD may be unable to properly checkthe layer 723 and/or picture 725 for conformance. This may result inencoding errors caused by the HRD and/or errors when decoding at adecoder. For example, the HRD may filter the picture improperly and/orfail to detect standards violations. Further, a decoder may fail todetect transmission related coding errors and/or improperly return anindication of a transmission related coding error when no such errorsexist.

Bitstream 700 is modified to ensure the SEI messages 719 are correctlyassociated with corresponding layers 723, pictures 725, slices 727,and/or NAL units. As described with respect to FIG. 6, multilayerbitstreams may organize pictures and associated parameters into AUs. AnAU is a set of coded pictures that are included in different layers andare associated with the same output time. In bitstream 700, each SEImessage 719 is positioned in the same AU as the first picture 725associated with the SEI message 719. Further, the SEI message 719 isassigned a TemporalId. The TemporalId of the SEI message 719 isconstrained to be equal to the TemporalId of the AU that contains theSEI message 719. In a particular example, each picture 725 in an AUshares the same value of TemporalId and hence share the same value ofnuh_temporal_id_plus1 731. Thus, the nuh_temporal_id_plus1 731 of theSEI message 719 is the same as the nuh_temporal_id_plus1 731 of each ofthe pictures 725 that correspond to which the SEI message 719 applies.

Stated differently, the pictures 725 are included in VCL NAL units 745and parameters are included in non-VCL NAL units 741. When the non-VCLNAL unit 741 is an SEI NAL unit of type PREFIX_SEI_NUT 742 orSUFFIX_SEI_NUT 743 that contains an SEI message 719, theTemporalId/nuh_temporal_id_plus1 731 of the non-VCL NAL unit 741 isconstrained to be equal to the TemporalId/nuh_temporal_id_plus1 731 ofthe AU containing the non-VCL NAL unit 741. This approach ensures thatthe SEI messages 719 are correctly associated with correspondingpictures 725 in the AUs. Hence, various errors may be avoided. As aresult, the functionality of the encoder and the decoder is increased.Further, coding efficiency may be increased, which reduces processor,memory, and/or network signaling resource usage at both the encoder andthe decoder.

The preceding information is now described in more detail herein below.Layered video coding is also referred to as scalable video coding orvideo coding with scalability. Scalability in video coding may besupported by using multi-layer coding techniques. A multi-layerbitstream comprises a base layer (BL) and one or more enhancement layers(ELs). Example of scalabilities includes spatial scalability,quality/signal to noise ratio (SNR) scalability, multi-view scalability,frame rate scalability, etc. When a multi-layer coding technique isused, a picture or a part thereof may be coded without using a referencepicture (intra-prediction), may be coded by referencing referencepictures that are in the same layer (inter-prediction), and/or may becoded by referencing reference pictures that are in other layer(s)(inter-layer prediction). A reference picture used for inter-layerprediction of the current picture is referred to as an inter-layerreference picture (ILRP). FIG. 6 illustrates an example of multi-layercoding for spatial scalability in which pictures in different layershave different resolutions.

Some video coding families provide support for scalability in separatedprofile(s) from the profile(s) for single-layer coding. Scalable videocoding (SVC) is a scalable extension of the advanced video coding (AVC)that provides support for spatial, temporal, and quality scalabilities.For SVC, a flag is signaled in each macroblock (MB) in EL pictures toindicate whether the EL MB is predicted using the collocated block froma lower layer. The prediction from the collocated block may includetexture, motion vectors, and/or coding modes. Implementations of SVC maynot directly reuse unmodified AVC implementations in their design. TheSVC EL macroblock syntax and decoding process differs from the AVCsyntax and decoding process.

Scalable HEVC (SHVC) is an extension of HEVC that provides support forspatial and quality scalabilities. Multiview HEVC (MV-HEVC) is anextension of HEVC that provides support for multi-view scalability. 3DHEVC (3D-HEVC) is an extension of HEVC that provides support for 3Dvideo coding that is more advanced and more efficient than MV-HEVC.Temporal scalability may be included as an integral part of asingle-layer HEVC codec. In the multi-layer extension of HEVC, decodedpictures used for inter-layer prediction come only from the same AU andare treated as long-term reference pictures (LTRPs). Such pictures areassigned reference indices in the reference picture list(s) along withother temporal reference pictures in the current layer. Inter-layerprediction (ILP) is achieved at the prediction unit level by setting thevalue of the reference index to refer to the inter-layer referencepicture(s) in the reference picture list(s). Spatial scalabilityresamples a reference picture or part thereof when an ILRP has adifferent spatial resolution than the current picture being encoded ordecoded. Reference picture resampling can be realized at either picturelevel or coding block level.

VVC may also support layered video coding. A VVC bitstream can includemultiple layers. The layers can be all independent from each other. Forexample, each layer can be coded without using inter-layer prediction.In this case, the layers are also referred to as simulcast layers. Insome cases, some of the layers are coded using ILP. A flag in the VPScan indicate whether the layers are simulcast layers or whether somelayers use ILP. When some layers use ILP, the layer dependencyrelationship among layers is also signaled in the VPS. Unlike SHVC andMV-HEVC, VVC may not specify OLSs. An OLS includes a specified set oflayers, where one or more layers in the set of layers are specified tobe output layers. An output layer is a layer of an OLS that is output.In some implementations of VVC, only one layer may be selected fordecoding and output when the layers are simulcast layers. In someimplementations of VVC, the entire bitstream including all layers isspecified to be decoded when any layer uses ILP. Further, certain layersamong the layers are specified to be output layers. The output layersmay be indicated to be only the highest layer, all the layers, or thehighest layer plus a set of indicated lower layers.

The preceding aspects contain certain problems. For example, thenuh_layer_id values for SPS, PPS, and APS NAL units may not be properlyconstrained. Further, the TemporalId value for SEI NAL units may not beproperly constrained. In addition, setting of NoOutputOfPriorPicsFlagmay not be properly specified when reference picture resampling isenabled and pictures within a CLVS have different spatial resolutions.Also, in some video coding systems suffix SEI messages cannot becontained in a scalable nesting SEI message. As another example,buffering period, picture timing, and decoding unit information SEImessages may include parsing dependencies on VPS and/or SPS.

In general, this disclosure describes video coding improvementapproaches. The descriptions of the techniques are based on VVC.However, the techniques also apply to layered video coding based onother video codec specifications.

One or more of the abovementioned problems may be solved as follows. Thenuh_layer_id values for SPS, PPS, and APS NAL units are properlyconstrained herein. The TemporalId value for SEI NAL units is properlyconstrained herein. Setting of the NoOutputOfPriorPicsFlag is properlyspecified when reference picture resampling is enabled and pictureswithin a CLVS have different spatial resolutions. Suffix SEI messagesare allowed to be contained in a scalable nesting SEI message. Parsingdependencies of BP, PT, and DUI SEI messages on VPS or SPS may beremoved by repeating the syntax elementdecoding_unit_hrd_params_present_flag in the BP SEI message syntax, thesyntax elements decoding_unit_hrd_params_present_flag anddecoding_unit_cpb_params_in_pic_timing_sei_flag in the PT SEI messagesyntax, and the syntax elementdecoding_unit_cpb_params_in_pic_timing_sei_flag in the DUI SEI message.

An example implementation of the preceding mechanisms is as follows. Anexample general NAL unit semantics is as follows.

A nuh_temporal_id_plus1 minus 1 specifies a temporal identifier for theNAL unit. The value of nuh_temporal_id_plus1 should not be equal tozero. The variable TemporalId may be derived as follows:

TemporalId = nuh_temporal_id_plus1 − 1

When nal_unit_type is in the range of IDR_W_RADL to RSV_IRAP_13,inclusive, TemporalId should be equal to zero. When nal_unit_type isequal to STSA_NUT, TemporalId should not be equal to zero.

The value of TemporalId should be the same for all VCL NAL units of anaccess unit. The value of TemporalId of a coded picture, a layer accessunit, or an access unit may be the value of the TemporalId of the VCLNAL units of the coded picture, the layer access unit, or the accessunit. The value of TemporalId of a sub-layer representation may be thegreatest value of TemporalId of all VCL NAL units in the sub-layerrepresentation.

The value of TemporalId for non-VCL NAL units is constrained as follows.If nal_unit_type is equal to DPS_NUT, VPS_NUT, or SPS_NUT, TemporalId isequal to zero and the TemporalId of the access unit containing the NALunit should be equal to zero. Otherwise if nal_unit_type is equal toEOS_NUT or EOB_NUT, TemporalId should be equal to zero. Otherwise, ifnal_unit_type is equal to AUD_NUT, FD_NUT, PREFIX_SEI_NUT, orSUFFIX_SEI_NUT, TemporalId should be equal to the TemporalId of theaccess unit containing the NAL unit. Otherwise, when nal_unit_type isequal to PPS NUT or APS NUT, TemporalId should be greater than or equalto the TemporalId of the access unit containing the NAL unit. When theNAL unit is a non-VCL NAL unit, the value of TemporalId should be equalto the minimum value of the TemporalId values of all access units towhich the non-VCL NAL unit applies. When nal_unit_type is equal toPPS_NUT or APS_NUT, TemporalId may be greater than or equal to theTemporalId of the containing access unit. This is because all PPSs andAPSs may be included in the beginning of a bitstream. Further, the firstcoded picture has TemporalId equal to zero.

An example sequence parameter set RBSP semantics is as follows. An SPSRBSP should be available to the decoding process prior to beingreferenced. The SPS may be included in at least one access unit withTemporalId equal to zero or provided through external mechanism. The SPSNAL unit containing the SPS may be constrained to have a nuh_layer_idequal to the lowest nuh_layer_id value of PPS NAL units that refer tothe SPS.

An example picture parameter set RBSP semantics is as follows. A PPSRBSP should be available to the decoding process prior to beingreferenced. The PPS should be included in at least one access unit withTemporalId less than or equal to the TemporalId of the PPS NAL unit orprovided through external mechanism. The PPS NAL unit containing the PPSRBSP should have a nuh_layer_id equal to the lowest nuh_layer_id valueof the coded slice NAL units that refer to the PPS.

An example adaptation parameter set semantics is as follows. Each APSRBSP should be available to the decoding process prior to beingreferenced. The APS should also be included in at least one access unitwith TemporalId less than or equal to the TemporalId of the coded sliceNAL unit that refers the APS or provided through an external mechanism.An APS NAL unit is allowed to be shared by pictures/slices of multiplelayers. The nuh_layer_id of an APS NAL unit should be equal to thelowest nuh_layer_id value of the coded slice NAL units that refer to theAPS NAL unit. Alternatively, an APS NAL unit may not be shared bypictures/slices of multiple layers. The nuh_layer_id of an APS NAL unitshould be equal to the nuh_layer_id of slices referring to the APS.

In an example, removal of pictures from the DPB before decoding of thecurrent picture is discussed as follows. The removal of pictures fromthe DPB before decoding of the current picture (but after parsing theslice header of the first slice of the current picture) may occur at theCPB removal time of the first decoding unit of access unit n (containingthe current picture). This proceeds as follows. The decoding process forreference picture list construction is invoked and the decoding processfor reference picture marking is invoked.

When the current picture is a coded layer video sequence start (CLVSS)picture that is not picture zero, the following ordered steps areapplied. The variable NoOutputOfPriorPicsFlag is derived for the decoderunder test as follows. If the value of pic_width_max_in_luma_samples,pic_height_max_in_luma_samples, chroma_format_idc,separate_colour_plane_flag, bit_depth_luma_minus8,bit_depth_chroma_minus8 or sps_max_dec_pic_buffering_minus1 [Htid]derived from the SPS is different from the value ofpic_width_in_luma_samples, pic_height_in_luma_samples,chroma_format_idc, separate_colour_plane_flag, bit_depth_luma_minus8,bit_depth_chroma_minus8 or sps_max_dec_pic_buffering_minus1 [Htid],respectively, derived from the SPS referred to by the preceding picture,NoOutputOfPriorPicsFlag may be set to one by the decoder under test,regardless of the value of no_output_of_prior_pics_flag. It should benoted that, although setting NoOutputOfPriorPicsFlag equal tono_output_of_prior_pics_flag may be preferred under these conditions,the decoder under test is allowed to set NoOutputOfPriorPicsFlag to onein this case. Otherwise, NoOutputOfPriorPicsFlag may be set equal tono_output_of_prior_pics_flag.

The value of NoOutputOfPriorPicsFlag derived for the decoder under testis applied for the HRD, such that when the value ofNoOutputOfPriorPicsFlag is equal to 1, all picture storage buffers inthe DPB are emptied without output of the pictures they contain, and theDPB fullness is set equal to zero. When both of the following conditionsare true for any pictures k in the DPB, all such pictures k in the DPBare removed from the DPB. Picture k is marked as unused for reference,and picture k has PictureOutputFlag equal to zero or a corresponding DPBoutput time is less than or equal to the CPB removal time of the firstdecoding unit (denoted as decoding unit m) of the current picture n.This may occur when DpbOutputTime[k] is less than or equal toDuCpbRemovalTime[m]. For each picture that is removed from the DPB, theDPB fullness is decremented by one.

In an example, output and removal of pictures from the DPB is discussedas follows. The output and removal of pictures from the DPB before thedecoding of the current picture (but after parsing the slice header ofthe first slice of the current picture) may occur when the firstdecoding unit of the access unit containing the current picture isremoved from the CPB and proceeds as follows. The decoding process forreference picture list construction and decoding process for referencepicture marking are invoked.

If the current picture is a CLVSS picture that is not picture zero, thefollowing ordered steps are applied. The variableNoOutputOfPriorPicsFlag can be derived for the decoder under test asfollows. If the value of pic_width_max_in_luma_samples,pic_height_max_in_luma_samples, chroma_format_idc,separate_colour_plane_flag, bit_depth_luma_minus8,bit_depth_chroma_minus8 or sps_max_dec_pic_buffering_minus1[Htid]derived from the SPS is different from the value ofpic_width_in_luma_samples, pic_height_in_luma_samples,chroma_format_idc, separate_colour_plane_flag, bit_depth_luma_minus8,bit_depth_chroma_minus8 or sps_max_dec_pic_buffering_minus1 [Htid],respectively, derived from the SPS referred to by the preceding picture,NoOutputOfPriorPicsFlag may be set to one by the decoder under test,regardless of the value of no_output_of_prior_pics_flag. It should benoted that although setting NoOutputOfPriorPicsFlag equal tono_output_of_prior_pics_flag is preferred under these conditions, thedecoder under test can set NoOutputOfPriorPicsFlag to one in this case.Otherwise, NoOutputOfPriorPicsFlag can be set equal tono_output_of_prior_pics_flag.

The value of NoOutputOfPriorPicsFlag derived for the decoder under testcan be applied for the HRD as follows. If NoOutputOfPriorPicsFlag isequal to one, all picture storage buffers in the DPB are emptied withoutoutput of the pictures they contain and the DPB fullness is set equal tozero. Otherwise (NoOutputOfPriorPicsFlag is equal to zero), all picturestorage buffers containing a picture that is marked as not needed foroutput and unused for reference are emptied (without output) and allnon-empty picture storage buffers in the DPB are emptied by repeatedlyinvoking a bumping process and the DPB fullness is set equal to zero.

Otherwise (the current picture is not a CLVSS picture), all picturestorage buffers containing a picture which are marked as not needed foroutput and unused for reference are emptied (without output). For eachpicture storage buffer that is emptied, the DPB fullness is decrementedby one. When one or more of the following conditions are true, thebumping process is invoked repeatedly while further decrementing the DPBfullness by one for each additional picture storage buffer that isemptied until none of the following conditions are true. A condition isthat the number of pictures in the DPB that are marked as needed foroutput is greater than sps_max_num_reorder_pics[Htid]. Another conditionis that a sps_max_latency_increase_plus1 [Htid] is not equal to zero andthere is at least one picture in the DPB that is marked as needed foroutput for which the associated variable PicLatencyCount is greater thanor equal to SpsMaxLatencyPictures[Htid]. Another condition is that thenumber of pictures in the DPB is greater than or equal toSubDpbSize[Htid].

An example general SEI message syntax is as follows.

Descriptor sei_payload( payloadType, payloadSize ) {  if( nal_unit_type= = PREFIX_SEI_NUT )   if( payloadType = = 0 )    buffering_period(payloadSize )   else if( payloadType = = 1 )    pic_timing( payloadSize)   else if( payloadType = = 3 )    filler_payload( payloadSize )   elseif( payloadType = = 130 )    decoding_unit_info( payloadSize )   elseif( payloadType = = 133 )    scalable_nesting( payloadSize )   else if(payloadType = = 145 )    dependent_rap_indication( payloadSize )     //Specified in ITU-T H.SEI | ISO/IEC 23002-7.   else if( payloadType = =168 )    frame_field_info( payloadSize )   else    reserved_sei_message(payloadSize )  else /* nal_unit_type = = SUFFIX_SEI_NUT */   if(payloadType = = 3 )    filler_payload( payloadSize )   if( payloadType == 132 )    decoded_picture_hash( payloadSize )     // Specified in ITU-TH.SEI | ISO/IEC 23002-7.   else if( payloadType = = 133 )   scalable_nesting( payloadSize )   else    reserved_sei_message(payloadSize )  if( more_data_in_payload( ) ) {   if(payload_extension_present( ) )    reserved_payload_extension_data u(v)  payload_bit_equal_to_one /* equal to 1 */ f(1)   while( !byte_aligned() )    payload_bit_equal_to_zero /* equal to 0 */ f(1)  } }

An example scalable nesting SEI message syntax is as follows.

Descriptor scalable_nesting( payloadSize ) {  nesting_ols_flag u(1)  if(nesting_ols_flag ) {   nesting_num_olss_minus1 ue(v)   for( i = 0; i <=nesting_num_olss_minus1; i++ ) {    nesting_ols_idx_delta_minus1[ i ]ue(v)    if( NumLayersInOls[ NestingOlsIdx[ i ] ] > 1 ) {    nesting_num_ols_layers_minus1[ i ] ue(v)     for( j = 0; j <=nesting_num_ols_layers_minus1[ i ]; j++ )     nesting_ols_layer_idx_delta_minus1[ i ][ j ] ue(v)    }   }  } else{   nesting_all_layers_flag u(1)   if( !nesting_all_layers_flag ) {   nesting_num_layers_minus1 ue(v)    for( i = 1; i <=nesting_num_layers_minus1; i++ )     nesting_layer_id[ i ] u(6)   }  } nesting_num_seis_minus1 ue(v)  while( !byte_aligned( ) )  nesting_zero_bit /* equal to 0 */ u(1)  for(i = 0; i <=nesting_num_seis_minus1; i++ )   sei_message( ) }

An example scalable nesting SEI message semantics is as follows. Ascalable nesting SEI message provides a mechanism to associate SEImessages with specific layers in the context of specific OLSs or withspecific layers not in the context of an OLS. A scalable nesting SEImessage contains one or more SEI messages. The SEI messages contained inthe scalable nesting SEI message are also referred to as thescalable-nested SEI messages. Bitstream conformance may require that thefollowing restrictions apply when SEI messages are contained in ascalable nesting SEI message.

An SEI message that has payloadType equal to one hundred thirty two(decoded picture hash) or one hundred thirty three (scalable nesting)should not be contained in a scalable nesting SEI message. When ascalable nesting SEI message contains a buffering period, picturetiming, or decoding unit information SEI message, the scalable nestingSEI message should not contain any other SEI message with payloadTypenot equal to zero (buffering period), one (picture timing), or onehundred thirty (decoding unit information).

Bitstream conformance may also require that the following restrictionsapply on the value of the nal_unit_type of the SEI NAL unit containing ascalable nesting SEI message. When a scalable nesting SEI messagecontains an SEI message that has payloadType equal to zero (bufferingperiod), one (picture timing), one hundred thirty (decoding unitinformation), one hundred forty five (dependent RAP indication), or onehundred sixty eight (frame-field information), the SEI NAL unitcontaining the scalable nesting SEI message should have a nal_unit_typeset equal to PREFIX_SEI_NUT. When a scalable nesting SEI messagecontains an SEI message that has payloadType equal to one hundred thirtytwo (decoded picture hash), the SEI NAL unit containing the scalablenesting SEI message should have a nal_unit_type set equal toSUFFIX_SEI_NUT.

A nesting_ols_flag may be set equal to one to specify that thescalable-nested SEI messages apply to specific layers in the context ofspecific OLSs. The nesting_ols_flag may be set equal to zero to specifythat that the scalable-nested SEI messages generally apply (e.g., not inthe context of an OLS) to specific layers.

Bitstream conformance may require that the following restrictions areapplied to the value of nesting_ols_flag. When the scalable nesting SEImessage contains an SEI message that has payloadType equal to zero(buffering period), one (picture timing), or one hundred thirty(decoding unit information), the value of nesting_ols_flag should beequal to one. When the scalable nesting SEI message contains an SEImessage that has payloadType equal to a value in VclAssociatedSeiList,the value of nesting_ols_flag should be equal to zero.

A nesting_num_olss_minus1 plus one specifies the number of OLSs to whichthe scalable-nested SEI messages apply. The value ofnesting_num_olss_minus1 should be in the range of zero toTotalNumOlss−1, inclusive. The nesting_ols_idx_delta_minus1[i] is usedto derive the variable NestingOlsIdx[i] that specifies the OLS index ofthe i-th OLS to which the scalable-nested SEI messages apply whennesting_ols_flag is equal to one. The value ofnesting_ols_idx_delta_minus1[i] should be in the range of zero toTotalNumOlss−2, inclusive. The variable NestingOlsIdx[i] may be derivedas follows:

if( i = = 0 )  NestingOlsIdx[ i ] = nesting_ols_idx_delta_minus1[ i ]else  NestingOlsIdx[ i ] = NestingOlsIdx[ i − 1 ] + nesting_ols_idx_delta_minus1[ i ] + 1

The nesting_num_ols_layers_minus1[i] plus one specifies the number oflayers to which the scalable-nested SEI messages apply in the context ofthe NestingOlsIdx[i]-th OLS. The value of nesting_num_ols_layers_minus1[i] should be in the range of zero toNumLayersInOls[NestingOlsIdx[i]]−1, inclusive.

The nesting_ols_layer_idx_delta_minus1[i][j] is used to derive thevariable NestingOlsLayerIdx[i][j] that specifies the OLS layer index ofthe j-th layer to which the scalable-nested SEI messages apply in thecontext of the NestingOlsIdx[i]-th OLS when nesting_ols_flag is equal toone. The value of nesting_ols_layer_idx_delta_minus1 [i] should be inthe range of zero to NumLayersInOls[nestingOlsIdx[i]]−two, inclusive.

The variable NestingOlsLayerIdx[i][j] may be derived as follows:

if( j = = 0 )  NestingOlsLayerIdx[ i ][ j ] = nesting_ols_layer_idx_delta_minus1[ i ][ j ] else  NestingOlsLayerIdx[i ][ j ] =  NestingOlsLayerIdx[ i ][ j − 1 ] +  nesting_ols_layer_idx_delta_minus1[ i ][ j ] + 1

The lowest value among all values ofLayerIdInOls[NestingOlsIdx[i]][NestingOlsLayerIdx[i][0]] for i in therange of zero to nesting_num_olss_minus1, inclusive, should be equal tonuh_layer_id of the current SEI NAL unit (e.g., the SEI NAL unitcontaining the scalable nesting SEI message). Thenesting_all_layers_flag may be set equal to one to specify that thescalable-nested SEI messages generally apply to all layers that havenuh_layer_id greater than or equal to the nuh_layer_id of the currentSEI NAL unit. The nesting_all_layers_flag may be set equal to zero tospecify that the scalable-nested SEI messages may or may not generallyapply to all layers that have nuh_layer_id greater than or equal to thenuh_layer_id of the current SEI NAL unit.

The nesting_num_layers_minus1 plus one specifies the number of layers towhich the scalable-nested SEI messages generally apply. The value ofnesting_num_layers_minus1 should be in the range of zero tovps_max_layers_minus1−GeneralLayerIdx[nuh_layer_id], inclusive, wherenuh_layer_id is the nuh_layer_id of the current SEI NAL unit. Thenesting_layer_id[i] specifies the nuh_layer_id value of the i-th layerto which the scalable-nested SEI messages generally apply whennesting_all_layers_flag is equal to zero. The value ofnesting_layer_id[i] should be greater than nuh_layer_id, wherenuh_layer_id is the nuh_layer_id of the current SEI NAL unit.

When the nesting_ols_flag is equal to one, the variableNestingNumLayers, specifying the number of layer to which thescalable-nested SEI messages generally apply, and the listNestingLayerId[i] for i in the range of zero to NestingNumLayers−1,inclusive, specifying the list of nuh_layer_id value of the layers towhich the scalable-nested SEI messages generally apply, are derived asfollows, where nuh_layer_id is the nuh_layer_id of the current SEI NALunit:

if( nesting_all_layers_flag ) {  NestingNumLayers =vps_max_layers_minus1 + 1 − GeneralLayerIdx[ nuh_layer_id ]  for( i = 0;i < NestingNumLayers; i ++)   NestingLayerId[ i ] =   vps_layer_id[GeneralLayerIdx[ nuh_layer_id ] + i ] (D-2) } else {  NestingNumLayers =nesting_num_layers_minus1 + 1  for( i = 0; i < NestingNumLayers; i ++)  NestingLayerId[ i ] = ( i = = 0 ) ?   nuh_layer_id : nesting_layer_id[i ] }

The nesting_num_seis_minus1 plus one specifies the number ofscalable-nested SEI messages. The value of nesting_num_seis_minus1should be in the range of zero to sixty three, inclusive. Thenesting_zero_bit should be set equal to zero.

FIG. 8 is a schematic diagram of an example video coding device 800. Thevideo coding device 800 is suitable for implementing the disclosedexamples/embodiments as described herein. The video coding device 800comprises downstream ports 820, upstream ports 850, and/or transceiverunits (Tx/Rx) 810, including transmitters and/or receivers forcommunicating data upstream and/or downstream over a network. The videocoding device 800 also includes a processor 830 including a logic unitand/or central processing unit (CPU) to process the data and a memory832 for storing the data. The video coding device 800 may also compriseelectrical, optical-to-electrical (OE) components, electrical-to-optical(EO) components, and/or wireless communication components coupled to theupstream ports 850 and/or downstream ports 820 for communication of datavia electrical, optical, or wireless communication networks. The videocoding device 800 may also include input and/or output (I/O) devices 860for communicating data to and from a user. The I/O devices 860 mayinclude output devices such as a display for displaying video data,speakers for outputting audio data, etc. The I/O devices 860 may alsoinclude input devices, such as a keyboard, mouse, trackball, etc.,and/or corresponding interfaces for interacting with such outputdevices.

The processor 830 is implemented by hardware and software. The processor830 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), field-programmable gate arrays (FPGAs),application specific integrated circuits (ASICs), and digital signalprocessors (DSPs). The processor 830 is in communication with thedownstream ports 820, Tx/Rx 810, upstream ports 850, and memory 832. Theprocessor 830 comprises a coding module 814. The coding module 814implements the disclosed embodiments described herein, such as methods100, 900, and 1000, which may employ a multi-layer video sequence 600and/or a bitstream 700. The coding module 814 may also implement anyother method/mechanism described herein. Further, the coding module 814may implement a codec system 200, an encoder 300, a decoder 400, and/ora HRD 500. For example, the coding module 814 may be employed signaland/or read various parameters as described herein. Further, the codingmodule may be employed to encode and/or decode a video sequence based onsuch parameters. As such, the signaling changes described herein mayincrease the efficiency and/or avoid errors in the coding module 814.Accordingly, the coding module 814 may be configured to performmechanisms to address one or more of the problems discussed above.Hence, coding module 814 causes the video coding device 800 to provideadditional functionality and/or coding efficiency when coding videodata. As such, the coding module 814 improves the functionality of thevideo coding device 800 as well as addresses problems that are specificto the video coding arts. Further, the coding module 814 effects atransformation of the video coding device 800 to a different state.Alternatively, the coding module 814 can be implemented as instructionsstored in the memory 832 and executed by the processor 830 (e.g., as acomputer program product stored on a non-transitory medium).

The memory 832 comprises one or more memory types such as disks, tapedrives, solid-state drives, read only memory (ROM), random access memory(RAM), flash memory, ternary content-addressable memory (TCAM), staticrandom-access memory (SRAM), etc. The memory 832 may be used as anover-flow data storage device, to store programs when such programs areselected for execution, and to store instructions and data that are readduring program execution.

FIG. 9 is a flowchart of an example method 900 of encoding a videosequence into a bitstream, such as bitstream 700, by constrainingTemporalIds for SEI messages in the bitstream. Method 900 may beemployed by an encoder, such as a codec system 200, an encoder 300,and/or a video coding device 800 when performing method 100. Further,the method 900 may operate on a HRD 500 and hence may performconformance tests on a multi-layer video sequence 600.

Method 900 may begin when an encoder receives a video sequence anddetermines to encode that video sequence into a multi-layer bitstream,for example based on user input. At step 901, the encoder encodes acoded picture in one or more VCL NAL units in a bitstream. For example,the coded picture may be included in an AU in a layer. Further, theencoder can encode one or more layers including the coded picture into amulti-layer bitstream. A layer may include a set of VCL NAL units withthe same layer ID and associated non-VCL NAL units. For example, the setof VCL NAL units are part of a layer when the set of VCL NAL units allhave a particular value of nuh_layer_id. A layer may include a set ofVCL NAL units that contain video data of encoded pictures as well as anyparameter sets used to code such pictures. One or more of the layers maybe output layers. Layers that are not an output layer are encoded tosupport reconstructing the output layer(s), but such supporting layersare not intended for output at a decoder. In this way, the encoder canencode various combinations of layers for transmission to a decoder uponrequest. The layer can be transmitted as desired to allow the decoder toobtain different representations of the video sequence depending onnetwork conditions, hardware capabilities, and/or user settings.

At step 903, the encoder can encode one or more a non-VCL NAL units intothe bitstream. For example, the layer and/or set of layers also includevarious non-VCL NAL units. The non-VCL NAL units are associated with theset of VCL NAL units that all have a particular value of nuh_layer_id.Specifically, a non-VCL NAL unit is encoded such that a TemporalId forthe non-VCL NAL unit is constrained to be equal to a TemporalId of an AUcontaining the non-VCL NAL unit when a nal_unit_type of the non-VCL NALindicates a SEI message is included in the non-VCL NAL. Stateddifferently, a SEI message may be included in the same AU as the pictureto which the SEI applies. Accordingly, the TemporalId of the SEI messagecontained in a non-VCL NAL unit is constrained to be equal to theTemporalId of the AU that contains the SEI message/non-VCL NAL unit. Insome examples, the SEI message is a prefix SEI message, and hence thenal_unit_type of the non-VCL NAL is equal to a PREFIX_SEI_NUT. In someexamples, the SEI message is a suffix SEI message, and hence thenal_unit_type of the non-VCL NAL is equal to a SUFFIX_SEI_NUT. The

The TemporalId for the non-VCL NAL unit may be specified by anuh_temporal_id_plus1 syntax element in the non-VCL NAL unit. Likewise,the TemporalId for the AU may be specified by a nuh_temporal_id_plus1syntax element in a VCL NAL unit containing a slice of the coded picturein the AU. A TemporalId of the VCL NAL units is constrained to be thesame for all VCL NAL units in a same AU. Accordingly, anuh_temporal_id_plus1 syntax element of the VCL NAL units is constrainedto be the same for all VCL NAL units in a same AU. Hence, the value ofthe nuh_temporal_id_plus1 syntax element in the non-VCL NAL unitcontaining the SEI message is the same as the value of thenuh_temporal_id_plus1 syntax element in any VCL NAL unit in the same AUas the SEI message. The TemporalId for the non-VCL NAL unit is derivedas follows:

TemporalId = nuh_temporal_id_plus1 − 1.

In addition, the value of the nuh_temporal_id_plus1 for the non-VCL NALunit and the VCL NAL unit in the AU may not be set to zero as this wouldresult in a negative value of TemporalId. The preceding constraintsand/or requirements ensure that the bitstream conforms with, forexample, VVC or some other standard, modified as indicated herein.However, the encoder may also be capable of operating in other modeswhere it is not so constrained, such as when operating under a differentstandard or a different version of the same standard.

At step 905, the encoder employs a HRD to perform a set of bitstreamconformance tests on the bitstream based on the SEI message. The set mayinclude one or more conformance tests. For example, the HRD can employthe TemporalIds and/or nuh_temporal_id_plus1 values to correlate SEImessages to the pictures. Hence, the HRD can employ the parameters fromthe SEI message to perform one or more conformance tests on the codedpicture in the same AU as the SEI message. The encoder can then storethe bitstream for communication toward a decoder at step 907. Theencoder can also transmit the bitstream toward the decoder as desired.

FIG. 10 is a flowchart of an example method 1000 of decoding a videosequence from a bitstream, such as bitstream 700, where TemporalIds forthe SEI messages in the bitstream are constrained. Method 1000 may beemployed by a decoder, such as a codec system 200, a decoder 400, and/ora video coding device 800 when performing method 100. Further, method1000 may be employed on a multi-layer video sequence 600 that has beenchecked for conformance by a HRD, such as HRD 500.

Method 1000 may begin when a decoder begins receiving a bitstream ofcoded data representing a multi-layer video sequence, for example as aresult of method 900 and/or in response to a request by the decoder. Atstep 1001, the decoder receives a bitstream a bitstream comprising acoded picture in one or more VCL NAL units and a non-VCL NAL unit. Forexample, the coded picture may be included in an AU. Further, thebitstream may include one or more layers including the coded picture. Alayer may include a set of VCL NAL units with the same layer ID andassociated non-VCL NAL units. For example, the set of VCL NAL units arepart of a layer when the set of VCL NAL units all have a particularvalue of nuh_layer_id. A layer may include a set of VCL NAL units thatcontain video data of coded pictures as well as any parameter sets usedto code such pictures. One or more of the layers may be output layers.Layers that are not an output layer are encoded to supportreconstructing the output layer(s), but such supporting layers are notintended for output. In this way, the decoder can obtain differentrepresentations of the video sequence depending on network conditions,hardware capabilities, and/or user settings. The layer also includesvarious non-VCL NAL units. The non-VCL NAL units are associated with theset of VCL NAL units that all have a particular value of nuh_layer_id.

Specifically, a non-VCL NAL unit is coded in the bitstream such that aTemporalId for the non-VCL NAL unit is constrained to be equal to aTemporalId of an AU containing the non-VCL NAL unit when a nal_unit_typeof the non-VCL NAL indicates a SEI message is included in the non-VCLNAL. Stated differently, a SEI message may be included in the same AU asthe picture to which the SEI applies. Accordingly, the TemporalId of theSEI message contained in a non-VCL NAL unit is constrained to be equalto the TemporalId of the AU that contains the SEI message/non-VCL NALunit. In some examples, the SEI message is a prefix SEI message, andhence the nal_unit_type of the non-VCL NAL is equal to a PREFIX_SEI_NUT.In some examples, the SEI message is a suffix SEI message, and hence thenal_unit_type of the non-VCL NAL is equal to a SUFFIX_SEI_NUT.

The TemporalId for the non-VCL NAL unit may be specified by anuh_temporal_id_plus1 syntax element in the non-VCL NAL unit.Accordingly, the decoder can derive the TemporalId for the non-VCL NALunit based on the nuh_temporal_id_plus1 syntax element in the non-VCLNAL unit at step 1002. Likewise, the TemporalId for the AU may bespecified by a nuh_temporal_id_plus1 syntax element in a VCL NAL unitcontaining a slice of the coded picture in the AU. A TemporalId of theVCL NAL units is constrained to be the same for all VCL NAL units in asame AU. Accordingly, a nuh_temporal_id_plus1 syntax element of the VCLNAL units is constrained to be the same for all VCL NAL units in a sameAU. Hence, the value of the nuh_temporal_id_plus1 syntax element in thenon-VCL NAL unit containing the SEI message is the same as the value ofthe nuh_temporal_id_plus1 syntax element in any VCL NAL unit in the sameAU as the SEI message. The TemporalId for the non-VCL NAL unit isderived as follows:

TemporalId = nuh_temporal_id_plus1 − 1.

In addition, the value of the nuh_temporal_id_plus1 for the non-VCL NALunit and the VCL NAL unit in the AU may not be set to zero as this wouldresult in a negative value of TemporalId.

In an embodiment, the video decoder expects a TemporalId for the non-VCLNAL unit to be equal to a TemporalId of an AU containing the non-VCL NALunit when a nal_unit_type of the non-VCL NAL is a SEI message asdescribed above based on VVC or some other standard. If, however, thedecoder determines that this condition is not true, the decoder maydetect an error, signal an error, request that a revised bitstream (or aportion thereof) be resent, or take some other corrective measures toensure that a conforming bitstream is received.

At step 1003, the decoder can decode the coded picture from the VCL NALunits to produce a decoded picture. For example, the decoder can employthe TemporalIds and/or nuh_temporal_id_plus1 values to correlate SEImessages to the pictures. The decoder can then employ the SEI messagesas desired when decoding the coded picture. At step 1005, the decodercan forward the decoded picture for display as part of a decoded videosequence.

FIG. 11 is a schematic diagram of an example system 1100 for coding avideo sequence using a bitstream where TemporalIds for the SEI messagesin the bitstream are constrained. System 1100 may be implemented by anencoder and a decoder such as a codec system 200, an encoder 300, adecoder 400, and/or a video coding device 800. Further, the system 1100may employ a HRD 500 to perform conformance tests on a multi-layer videosequence 600 and/or a bitstream 700. In addition, system 1100 may beemployed when implementing method 100, 900, and/or 1000.

The system 1100 includes a video encoder 1102. The video encoder 1102comprises an encoding module 1103 for encoding a coded picture in one ormore VCL NAL units in a bitstream. The encoding module 1103 is furtherfor encoding into the bitstream a non-VCL NAL unit such that aTemporalId for the non-VCL NAL unit is constrained to be equal to aTemporalId of an AU containing the non-VCL NAL unit when a nal_unit_typeof the non-VCL NAL is a SEI message. The video encoder 1102 furthercomprises a HRD module 1105 for performing a set of bitstreamconformance tests on the bitstream based on the SEI message. The videoencoder 1102 further comprises a storing module 1106 for storing thebitstream for communication toward a decoder. The video encoder 1102further comprises a transmitting module 1107 for transmitting thebitstream toward a video decoder 1110. The video encoder 1102 may befurther configured to perform any of the steps of method 900.

The system 1100 also includes a video decoder 1110. The video decoder1110 comprises a receiving module 1111 for receiving a bitstreamcomprising a coded picture in one or more VCL NAL units and a non-VCLNAL unit, wherein a TemporalId for the non-VCL NAL unit is constrainedto be equal to a TemporalId of an AU containing the non-VCL NAL unitwhen a nal_unit_type of the non-VCL NAL is a SEI message. The videodecoder 1110 further comprises a decoding module 1113 for decoding thecoded picture from the VCL NAL units to produce a decoded picture. Thevideo decoder 1110 further comprises a forwarding module 1115 forforwarding the decoded picture for display as part of a decoded videosequence. The video decoder 1110 may be further configured to performany of the steps of method 1000.

A first component is directly coupled to a second component when thereare no intervening components, except for a line, a trace, or anothermedium between the first component and the second component. The firstcomponent is indirectly coupled to the second component when there areintervening components other than a line, a trace, or another mediumbetween the first component and the second component. The term “coupled”and its variants include both directly coupled and indirectly coupled.The use of the term “about” means a range including ±10% of thesubsequent number unless otherwise stated.

It should also be understood that the steps of the exemplary methods setforth herein are not necessarily required to be performed in the orderdescribed, and the order of the steps of such methods should beunderstood to be merely exemplary. Likewise, additional steps may beincluded in such methods, and certain steps may be omitted or combined,in methods consistent with various embodiments of the presentdisclosure.

While several embodiments have been provided in the present disclosure,it may be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, components, techniques, ormethods without departing from the scope of the present disclosure.Other examples of changes, substitutions, and alterations areascertainable by one skilled in the art and may be made withoutdeparting from the spirit and scope disclosed herein.

What is claimed is:
 1. A method implemented by a decoder, the methodcomprising: receiving, by a receiver of the decoder, a bitstreamcomprising a coded picture in one or more video coding layer (VCL)network abstraction layer (NAL) units and a non-VCL NAL unit, wherein atemporal identifier (TemporalId) for the non-VCL NAL unit is constrainedto be equal to a TemporalId of an access unit (AU) containing thenon-VCL NAL unit when a NAL unit type (nal_unit_type) of the non-VCL NALis equal to a prefix supplemental enhancement information (SEI) NAL unittype (PREFIX_SEI_NUT) or a suffix SEI NAL unit type (SUFFIX_SEI_NUT);deriving, by a processor of the decoder, the TemporalId for the non-VCLNAL unit based on a NAL unit header temporal identifier plus one(nuh_temporal_id_plus1) syntax element in the non-VCL NAL unit; anddecoding, by the processor of the decoder, the coded picture from theVCL NAL units to produce a decoded picture.
 2. The method of claim 1,wherein the nal_unit_type of the non-VCL NAL is equal to thePREFIX_SEI_NUT.
 3. The method of claim 1, wherein the nal_unit_type ofthe non-VCL NAL is equal to the SUFFIX_SEI_NUT.
 4. The method of claim1, wherein the coded picture is decoded from the VCL NAL units based ona SEI message in the non-VCL NAL unit.
 5. The method of claim 1, furthercomprising deriving the TemporalId for the non-VCL NAL unit as follows:TemporalId = nuh_temporal_id_plus1 −
 1. 6. The method of claim 5,wherein a value of nuh_temporal_id_plus1 is not equal to zero.
 7. Themethod of claim 1, wherein a TemporalId of the VCL NAL units isconstrained to be the same for all VCL NAL units in a same AU.
 8. Themethod of claim 1, further comprising: receiving, by the decoder, asecond bitstream including a second one or more VCL NAL units and asecond non-VCL NAL unit, wherein a TemporalId for the second non-VCL NALunit is not equal to a TemporalId of a second AU containing the secondnon-VCL NAL unit when a nal_unit_type of the second non-VCL NAL is a SEImessage; and in response to the receiving, taking some other correctivemeasures to ensure that a conforming bitstream corresponding to thesecond bitstream is received prior to decoding the coded picture fromthe second VCL NAL units.
 9. A method implemented by an encoder, themethod comprising: encoding, by a processor of the encoder, a codedpicture in one or more video coding layer (VCL) network abstractionlayer (NAL) units in a bitstream; encoding into the bitstream, by theprocessor, a non-VCL NAL unit such that a NAL unit header temporalidentifier plus one (nuh_temporal_id_plus1) for the non-VCL NAL unit isconstrained to be equal to a nuh_temporal_id_plus1 of an access unit(AU) containing the non-VCL NAL unit when a NAL unit type(nal_unit_type) of the non-VCL NAL is a supplemental enhancementinformation (SEI) message; performing, by the processor, a set ofbitstream conformance tests on the bitstream based on the SEI message;and storing, by a memory coupled to the processor, the bitstream forcommunication toward a decoder.
 10. The method of claim 9, wherein thenal_unit_type of the non-VCL NAL is equal to a prefix SEI NAL unit type(PREFIX_SEI_NUT).
 11. The method of claim 9, wherein the nal_unit_typeof the non-VCL NAL is equal to a suffix SEI NAL unit type(SUFFIX_SEI_NUT).
 12. The method of claim 9, wherein a value ofnuh_temporal_id_plus1 is not equal to zero.
 13. The method of claim 9,wherein a nuh_temporal_id_plus1 of the VCL NAL units is constrained tobe the same for all VCL NAL units in a same AU.
 14. A video codingdevice comprising: a receiver configured to receive a bitstreamcomprising a coded picture in one or more video coding layer (VCL)network abstraction layer (NAL) units and a non-VCL NAL unit, wherein atemporal identifier (TemporalId) for the non-VCL NAL unit is constrainedto be equal to a TemporalId of an access unit (AU) containing thenon-VCL NAL unit when a NAL unit type (nal_unit_type) of the non-VCL NALis equal to a prefix supplemental enhancement information (SEI) NAL unittype (PREFIX_SEI_NUT) or a suffix SEI NAL unit type (SUFFIX_SEI_NUT); aprocessor coupled to the receiver and configured to: derive theTemporalId for the non-VCL NAL unit based on a NAL unit header temporalidentifier plus one (nuh_temporal_id_plus1) syntax element in thenon-VCL NAL unit; and decode the coded picture from the VCL NAL units toproduce a decoded picture.
 15. The video coding device of claim 14,wherein the nal_unit_type of the non-VCL NAL is equal to thePREFIX_SEI_NUT.
 16. The video coding device of claim 15, wherein thenal_unit_type of the non-VCL NAL is equal to the SUFFIX_SEI_NUT.
 17. Thevideo coding device of claim 16, wherein the coded picture is decodedfrom the VCL NAL units based on a SEI message in the non-VCL NAL unit.18. The video coding device of claim 17, further comprising deriving theTemporalId for the non-VCL NAL unit as follows:TemporalId = nuh_temporal_id_plus1 −
 1. 19. The video coding device ofclaim 18, wherein a value of nuh_temporal_id_plus1 is not equal to zero.20. The video coding device of claim 14, wherein a TemporalId of the VCLNAL units is constrained to be the same for all VCL NAL units in a sameAU.